As @Ladsgroup pointed out here: T238966#6152150 we are seeing errors as there's a piece of code that forces to use user_timestamp index.
A database query error has occurred. Did you forget to run your application's database schema updater after upgrading? Query: SELECT rev_id,rev_page,rev_timestamp,rev_minor_edit,rev_deleted,rev_len,rev_parent_id,rev_sha1,comment_rev_comment.comment_text AS `rev_comment_text`,comment_rev_comment.comment_data AS `rev_comment_data`,comment_rev_comment.comment_id AS `rev_comment_cid`,actor_rev_user.actor_user AS `rev_user`,actor_rev_user.actor_name AS `rev_user_text`,temp_rev_user.revactor_actor AS `rev_actor`,page_namespace,page_title,page_id,page_latest,page_is_redirect,page_len,user_name,page_is_new,(SELECT GROUP_CONCAT(ctd_name SEPARATOR ',') FROM `change_tag` JOIN `change_tag_def` ON ((ct_tag_id=ctd_id)) WHERE ct_rev_id=rev_id ) AS `ts_tags` FROM `revision` FORCE INDEX (usertext_timestamp) JOIN `revision_comment_temp` `temp_rev_comment` ON ((temp_rev_comment.revcomment_rev = rev_id)) JOIN `comment` `comment_rev_comment` ON ((comment_rev_comment.comment_id = temp_rev_comment.revcomment_comment_id)) JOIN `revision_actor_temp` `temp_rev_user` ON ((temp_rev_user.revactor_rev = rev_id)) JOIN `actor` `actor_rev_user` ON ((actor_rev_user.actor_id = temp_rev_user.revactor_actor)) JOIN `page` ON ((page_id = rev_page)) LEFT JOIN `user` ON ((actor_rev_user.actor_user != 0) AND (user_id = actor_rev_user.actor_user)) WHERE (1=0) AND ((rev_deleted & 4) = 0) ORDER BY rev_timestamp DESC,rev_id DESC LIMIT 51 Function: IndexPager::buildQueryInfo (contributions page unfiltered) Error: 1176 Key 'usertext_timestamp' doesn't exist in table 'revision' (10.64.16.7)
As new wikis do not include this index per the schema change merged at https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/552339/19/maintenance/archives/patch-revision-actor-comment-MCR.sql this is producing errors.
This force needs to be removed in code before we can proceed with the schema change in production.
Ideally we should review all the index that are being dropped to make sure none of those are being forced as well.
From revision, user_timestamp, page_user_timestamp and usertext_timestamp should all be evaluated and cleaned up, including various comment usages