We have updated to MW 1.35.4 recently, additionally we switched to PHP 7.4.24.
When running with PHP 7.4, the script begins checking external links and after some thousand or more it crashes:
InvalidArgumentException from line 152 of /var/www/test/mediawiki/vendor/guzzlehttp/psr7/src/Response.php: Status code must be an integer value between 1xx and 5xx.
#0 /var/www/test/mediawiki/vendor/guzzlehttp/psr7/src/Response.php(99): GuzzleHttp\Psr7\Response->assertStatusCodeRange()
#1 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/Handler/StreamHandler.php(115): GuzzleHttp\Psr7\Response->__construct()
#2 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/Handler/StreamHandler.php(50): GuzzleHttp\Handler\StreamHandler->createResponse()
#3 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/Middleware.php(233): GuzzleHttp\Handler\StreamHandler->__invoke()
#4 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/PrepareBodyMiddleware.php(37): GuzzleHttp\Middleware::GuzzleHttp\{closure}()
#5 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/RedirectMiddleware.php(54): GuzzleHttp\PrepareBodyMiddleware->__invoke()
#6 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/Middleware.php(57): GuzzleHttp\RedirectMiddleware->__invoke()
#7 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/HandlerStack.php(71): GuzzleHttp\Middleware::GuzzleHttp\{closure}()
#8 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/Client.php(351): GuzzleHttp\HandlerStack->__invoke()
#9 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/Client.php(112): GuzzleHttp\Client->transfer()
#10 /var/www/test/mediawiki/vendor/guzzlehttp/guzzle/src/Client.php(129): GuzzleHttp\Client->sendAsync()
#11 /var/www/test/mediawiki/includes/http/GuzzleHttpRequest.php(204): GuzzleHttp\Client->send()
#12 /var/www/test/mediawiki/includes/libs/http/MultiHttpClient.php(500): GuzzleHttpRequest->execute()
#13 /var/www/test/mediawiki/includes/libs/http/MultiHttpClient.php(191): MultiHttpClient->runMultiHttp()
#14 /var/www/test/mediawiki/includes/libs/http/MultiHttpClient.php(145): MultiHttpClient->runMulti()
#15 /var/www/test/mediawiki/extensions/RottenLinks/includes/RottenLinks.php(25): MultiHttpClient->run()
#16 /var/www/test/mediawiki/extensions/RottenLinks/maintenance/updateExternalLinks.php(57): RottenLinks::getResponse()
#17 /var/www/test/mediawiki/maintenance/doMaintenance.php(107): UpdateExternalLinks->execute()
#18 /var/www/test/mediawiki/extensions/RottenLinks/maintenance/updateExternalLinks.php(83): require_once('/var/www/test/m...')
#19 {main}