Current lag is very likely caused by T352010: Gradually drop old pagelinks columns as shown on https://wikitech.wikimedia.org/wiki/Map_of_database_maintenance which is linked to by https://replag.toolforge.org/ prominently.

I'm going to close this because of that connection. If the lag persists for days we should nudge the DBAs to see if there is some other active issue that is not planned maintenance.