Thanks for the feedback. We actually only have 1 editor working part time, so I know there are rearely more than a few 100's of edits in any 2 week period and I compress every 2 weeks. The state_lineages table only has 158 rows/16 Kb, and I assume that is small. Regardless, for unknown reasons the edit_versions are now working at normal speed again today. Haven't even restarted the servers since the problem was diagnosed, so hoping it won't come up again... No way to further troubleshoot without it working either. Fingers crossed...
Thanks, Gavin