Use of SkinTemplateToolboxEnd hook (used in ShortUrlHooks::addToolboxLink) was deprecated in MediaWiki 1.35. [Called from MediaWiki\HookContainer\HookContainer::run in /srv/mediawiki/php-1.35.0-wmf.32/includes/HookContainer/HookContainer.php at line 132]
7,000+ warnings logged per hour to Logstash. And that's only with group1 traffic.
Most likely caused by https://gerrit.wikimedia.org/r/587536, which added a Hooks::run() call in Vector code, for a hook owned by core. It also called it with hard-deprecation (when the core hook isn't), leading to some confusion during the investigation into this.
The hook callsite needs to be un-deprecated, or the caller(s) migrated/removed.