Hi, a co-worker of @vintrax here.
It seems this happened because I messed up. I wrote a bot that accidentally left hundreds of comments in a single task in the span of 20 minutes. The large amount of comments caused both the a lot of search index jobs to be slow (DELETEs/UPDATEs on a big MYSQL record) and big in amount (an index job per comment). To top it off these jobs couldn't be run in parallel efficiently because of search_documentfield table locks (because it's MyISAM). This caused the queue to still be clogged more than 24 hours after the 'bot mishap' happened, which is why I initially did not think this had caused the issues