As of now, hywwiki has Add Link backend enabled, and the refreshLinkRecommendations job is trying to populate its pool:
[urbanecm@mwmaint1002 /var/log/mediawiki/mediawiki_job_growthexperiments-refreshLinkRecommendations-s3]$ grep -h -F hywwiki syslog.log* | head Jul 11 07:24:29 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: Refreshing link recommendations... Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: processing topic biography... Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: 500 new tasks needed Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: fetching 500 tasks... Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: checking candidate Սարգիս_Արարատեան... There was a problem during the HTTP request: 400 Bad Request Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: checking candidate Էրեբունի_թանգարան_եւ_երեգան_թանգարան... There was a problem during the HTTP request: 400 Bad Request Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: checking candidate Աղաւնոյ_Գիւղ... There was a problem during the HTTP request: 400 Bad Request Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: checking candidate 1676_թուական... There was a problem during the HTTP request: 400 Bad Request Jul 11 07:24:30 mwmaint1002 mediawiki_job_growthexperiments-refreshLinkRecommendations-s3[8417]: hywwiki: checking candidate Սամուէլ_Ակոբ_Ուլուչեան... There was a problem during the HTTP request: 400 Bad Request [urbanecm@mwmaint1002 /var/log/mediawiki/mediawiki_job_growthexperiments-refreshLinkRecommendations-s3]$
Those attempts fail, because hywwiki does not have add link models (they did not pass recall and precision thresholds; see T309263 and T308134#8548734). Since the models are unavailable for hywwiki, there is no point in trying to populate the task pool, since it is not going to be available in the near future. For this reason, we should disable Add Link backend on hywwiki.