@craftxbox LinkCrawlWorker will be triggered for pretty much every link that shows up in an incoming post, as for SynchronizeFeaturedCollectionWorker, you can see which user it is for by taking the ID in arguments and going to /admin/accounts/<id>, IIRC
could be one of the denial of service attack servers that's shown up recently, or just that you're getting a lot of legitimate incoming traffic from relays, for example.