diff --git a/src/App.php b/src/App.php
index 25770dd782..0d4e8880dd 100644
--- a/src/App.php
+++ b/src/App.php
@@ -631,10 +631,10 @@ class App
 
 			// ZRL
 			if (!empty($_GET['zrl']) && $this->mode->isNormal() && !$this->mode->isBackend() && !$this->session->getLocalUserId()) {
-				// Only continue when the given profile link seems valid
+				// Only continue when the given profile link seems valid.
 				// Valid profile links contain a path with "/profile/" and no query parameters
 				if ((parse_url($_GET['zrl'], PHP_URL_QUERY) == '') &&
-					strstr(parse_url($_GET['zrl'], PHP_URL_PATH), '/profile/')) {
+					strpos(parse_url($_GET['zrl'], PHP_URL_PATH) ?? '', '/profile/') !== false) {
 					if ($this->session->get('visitor_home') != $_GET['zrl']) {
 						$this->session->set('my_url', $_GET['zrl']);
 						$this->session->set('authenticated', 0);
diff --git a/src/Contact/Avatar.php b/src/Contact/Avatar.php
index 0cfc8df345..711a8549f2 100644
--- a/src/Contact/Avatar.php
+++ b/src/Contact/Avatar.php
@@ -125,7 +125,7 @@ class Avatar
 
 	private static function getFilename(string $url): string
 	{
-		$guid = Item::guidFromUri($url, parse_url($url, PHP_URL_HOST));
+		$guid = Item::guidFromUri($url);
 
 		return substr($guid, 0, 2) . '/' . substr($guid, 3, 2) . '/' . substr($guid, 5, 3) . '/' .
 			substr($guid, 9, 2) .'/' . substr($guid, 11, 2) . '/' . substr($guid, 13, 4). '/' . substr($guid, 18) . '-';
diff --git a/src/Model/APContact.php b/src/Model/APContact.php
index 67ce2b66bf..fd748f1cd4 100644
--- a/src/Model/APContact.php
+++ b/src/Model/APContact.php
@@ -291,14 +291,11 @@ class APContact
 			return $fetched_contact;
 		}
 
-		$parts = parse_url($apcontact['url']);
-		unset($parts['scheme']);
-		unset($parts['path']);
-
 		if (empty($apcontact['addr'])) {
-			if (!empty($apcontact['nick']) && is_array($parts)) {
-				$apcontact['addr'] = $apcontact['nick'] . '@' . str_replace('//', '', Network::unparseURL($parts));
-			} else {
+			try {
+				$apcontact['addr'] = $apcontact['nick'] . '@' . (new Uri($apcontact['url']))->getAuthority();
+			} catch (\Throwable $e) {
+				Logger::warning('Unable to coerce APContact URL into a UriInterface object', ['url' => $apcontact['url'], 'error' => $e->getMessage()]);
 				$apcontact['addr'] = '';
 			}
 		}
diff --git a/src/Model/Contact.php b/src/Model/Contact.php
index 873de08906..4a10fd98ea 100644
--- a/src/Model/Contact.php
+++ b/src/Model/Contact.php
@@ -2099,7 +2099,7 @@ class Contact
 		if ($static) {
 			$query_params['static'] = true;
 		}
-		
+
 		return $url . ($guid ?: $cid) . (!empty($query_params) ? '?' . http_build_query($query_params) : '');
 	}
 
@@ -2675,7 +2675,7 @@ class Contact
 		}
 
 		$update = false;
-		$guid = ($ret['guid'] ?? '') ?: Item::guidFromUri($ret['url'], parse_url($ret['url'], PHP_URL_HOST));
+		$guid = ($ret['guid'] ?? '') ?: Item::guidFromUri($ret['url']);
 
 		// make sure to not overwrite existing values with blank entries except some technical fields
 		$keep = ['batch', 'notify', 'poll', 'request', 'confirm', 'poco', 'baseurl'];
diff --git a/src/Model/Item.php b/src/Model/Item.php
index ff4791a7cc..8b9909f8bf 100644
--- a/src/Model/Item.php
+++ b/src/Model/Item.php
@@ -2034,9 +2034,10 @@ class Item
 	 * Posts that are created on this system are using System::createUUID.
 	 * Received ActivityPub posts are using Processor::getGUIDByURL.
 	 *
-	 * @param string      $uri uri of an item entry
+	 * @param string      $uri  uri of an item entry
 	 * @param string|null $host hostname for the GUID prefix
 	 * @return string Unique guid
+	 * @throws \Exception
 	 */
 	public static function guidFromUri(string $uri, string $host = null): string
 	{
@@ -2047,11 +2048,16 @@ class Item
 		// Remove the scheme to make sure that "https" and "http" doesn't make a difference
 		unset($parsed['scheme']);
 
+		$hostPart = $host ?? $parsed['host'] ?? '';
+		if (!$hostPart) {
+			Logger::warning('Empty host GUID part', ['uri' => $uri, 'host' => $host, 'parsed' => $parsed, 'callstack' => System::callstack(10)]);
+		}
+
 		// Glue it together to be able to make a hash from it
 		$host_id = implode('/', $parsed);
 
 		// Use a mixture of several hashes to provide some GUID like experience
-		return hash('crc32', $host) . '-'. hash('joaat', $host_id) . '-'. hash('fnv164', $host_id);
+		return hash('crc32', $hostPart) . '-' . hash('joaat', $host_id) . '-' . hash('fnv164', $host_id);
 	}
 
 	/**
diff --git a/src/Model/Mail.php b/src/Model/Mail.php
index 6ccce24ba7..9469483d9a 100644
--- a/src/Model/Mail.php
+++ b/src/Model/Mail.php
@@ -59,8 +59,7 @@ class Mail
 		}
 
 		if (empty($msg['guid'])) {
-			$host = parse_url($msg['from-url'], PHP_URL_HOST);
-			$msg['guid'] = Item::guidFromUri($msg['uri'], $host);
+			$msg['guid'] = Item::guidFromUri($msg['uri'], parse_url($msg['from-url'], PHP_URL_HOST));
 		}
 
 		$msg['created'] = (!empty($msg['created']) ? DateTimeFormat::utc($msg['created']) : DateTimeFormat::utcNow());
diff --git a/src/Module/NoScrape.php b/src/Module/NoScrape.php
index 8e5850ac0b..56f31f2dcf 100644
--- a/src/Module/NoScrape.php
+++ b/src/Module/NoScrape.php
@@ -94,7 +94,7 @@ class NoScrape extends BaseModule
 
 		// We display the last activity (post or login), reduced to year and week number
 		$last_active = strtotime($owner['last-item']);
-		if ($last_active < strtotime($owner['last-activity'])) {
+		if ($owner['last-activity'] && $last_active < strtotime($owner['last-activity'])) {
 			$last_active = strtotime($owner['last-activity']);
 		}
 		$json_info['last-activity'] = date('o-W', $last_active);
diff --git a/src/Module/Tos.php b/src/Module/Tos.php
index 822aa8813b..11cecac44d 100644
--- a/src/Module/Tos.php
+++ b/src/Module/Tos.php
@@ -77,7 +77,7 @@ class Tos extends BaseModule
 	 */
 	protected function content(array $request = []): string
 	{
-		if (strlen($this->config->get('system', 'singleuser'))) {
+		if ($this->config->get('system', 'singleuser')) {
 			$this->baseUrl->redirect('profile/' . $this->config->get('system', 'singleuser'));
 		}
 
diff --git a/src/Network/Probe.php b/src/Network/Probe.php
index 5beef2ea82..5a8f75e2d8 100644
--- a/src/Network/Probe.php
+++ b/src/Network/Probe.php
@@ -687,7 +687,7 @@ class Probe
 		}
 
 		$parts = parse_url($uri);
-		if (empty($parts['scheme']) && empty($parts['host']) && !strstr($parts['path'], '@')) {
+		if (empty($parts['scheme']) && empty($parts['host']) && (empty($parts['path']) || strpos($parts['path'], '@') === false)) {
 			Logger::info('URI was not detectable', ['uri' => $uri]);
 			return [];
 		}
diff --git a/src/Protocol/ActivityPub/Processor.php b/src/Protocol/ActivityPub/Processor.php
index 8e21a66446..d098ddb691 100644
--- a/src/Protocol/ActivityPub/Processor.php
+++ b/src/Protocol/ActivityPub/Processor.php
@@ -804,7 +804,7 @@ class Processor
 	private static function processContent(array $activity, array $item)
 	{
 		if (!empty($activity['mediatype']) && ($activity['mediatype'] == 'text/markdown')) {
-			$item['title'] = strip_tags($activity['name']);
+			$item['title'] = strip_tags($activity['name'] ?? '');
 			$content = Markdown::toBBCode($activity['content']);
 		} elseif (!empty($activity['mediatype']) && ($activity['mediatype'] == 'text/bbcode')) {
 			$item['title'] = $activity['name'];
@@ -1273,8 +1273,11 @@ class Processor
 				foreach ($receivers[$element] as $receiver) {
 					if ($receiver == ActivityPub::PUBLIC_COLLECTION) {
 						$name = Receiver::PUBLIC_COLLECTION;
+					} elseif ($path = parse_url($receiver, PHP_URL_PATH)) {
+						$name = trim($path, '/');
 					} else {
-						$name = trim(parse_url($receiver, PHP_URL_PATH), '/');
+						Logger::warning('Unable to coerce name from receiver', ['receiver' => $receiver]);
+						$name = '';
 					}
 
 					$target = Tag::getTargetType($receiver);
diff --git a/src/Protocol/ActivityPub/Receiver.php b/src/Protocol/ActivityPub/Receiver.php
index 4e2bcceafb..8939822742 100644
--- a/src/Protocol/ActivityPub/Receiver.php
+++ b/src/Protocol/ActivityPub/Receiver.php
@@ -209,7 +209,7 @@ class Receiver
 				Logger::notice('No object data found', ['type' => $type, 'object_type' => $object_type, 'object_id' => $object_id, 'actor' => $actor, 'activity' => $activity]);
 				return;
 			}
-	
+
 			if (self::routeActivities($object_data, $type, true)) {
 				Logger::debug('Handled activity', ['type' => $type, 'object_type' => $object_type, 'object_id' => $object_id, 'actor' => $actor]);
 			} else {
@@ -1472,7 +1472,7 @@ class Receiver
 				continue;
 			}
 
-			$element = ['type' => str_replace('as:', '', JsonLD::fetchElement($tag, '@type')),
+			$element = ['type' => str_replace('as:', '', JsonLD::fetchElement($tag, '@type') ?? ''),
 				'href' => JsonLD::fetchElement($tag, 'as:href', '@id'),
 				'name' => JsonLD::fetchElement($tag, 'as:name', '@value')];
 
diff --git a/src/Protocol/Feed.php b/src/Protocol/Feed.php
index 29b1923316..dec463820d 100644
--- a/src/Protocol/Feed.php
+++ b/src/Protocol/Feed.php
@@ -625,8 +625,8 @@ class Feed
 
 			$notify = Item::isRemoteSelf($contact, $item);
 
-			// Distributed items should have a well formatted URI.
-			// Additionally we have to avoid conflicts with identical URI between imported feeds and these items.
+			// Distributed items should have a well-formatted URI.
+			// Additionally, we have to avoid conflicts with identical URI between imported feeds and these items.
 			if ($notify) {
 				$item['guid'] = Item::guidFromUri($orig_plink, DI::baseUrl()->getHostname());
 				$item['uri'] = Item::newURI($item['guid']);