From a support desk posting (Error 1091: Can't DROP 'ipb_address_unique'), it looks like a migration from 1.31 to 1.35 might run into problems with T250071: Rename ipb_address index on ipb_address to ipb_address_unique:
# php maintenance/update.php --quick --skip-external-dependencies ... Updating length of lc_lang in `l10n_cache` ...done. Updating length of ll_lang in `langlinks` ...done. Updating length of site_language in `sites` ...done. ...skipping update to shared table ipblocks. Removing ipb_anon_only column from ipb_address_unique index ... Wikimedia\Rdbms\DBQueryError from line 1699 of /var/www/html/includes/libs/rdbms/database/Database.php: Error 1091: Can't DROP 'ipb_address_unique'; check that column/key exists (mysql) Function: Wikimedia\Rdbms\Database::sourceFile( /var/www/html/maintenance/archives/patch-ipblocks-fix-ipb_address_unique.sql ) Query: ALTER TABLE `zeus_de`.`ipblocks` DROP INDEX ipb_address_unique, ADD UNIQUE INDEX ipb_address_unique (ipb_address(255), ipb_user, ipb_auto ) ...