Try emptying your recycle bin and let us know if it helps.
No, that didn't help and no one has been able to resolve this issue.
I have read that sometimes the messages appears in error, that it shouldn't appear but it does.
Nevertheless, if your Lightroom is running slowly, then please tell us exactly what actions are slow in Lightroom. Be specific. Be detailed. Use the Lightroom name of the action.
And upgrade to Lr 6.12. If there is a bug, it may have been fixed since 6.8.