Collection shows previously removed photos after upgrade
I've just upgraded to Lightroom CC (2015.4-2015.8; from Dec 08) from previous Lightroom CC (2015.2-2015.3; from Oct 05).
Now the issue I have is that my collection shows photos which had been previously removed from the collection. For example I had a collection of e.g. 2000 photos flagged photos, I manually removed 500 photos during triage, now after the upgrade of Lightroom all 2000 photos show again in the collection.
I opened a few previous backups (I do daily backups) by double-clicking the lrcat file, but with same result.
Any idea how to solve this or anyone faced similar issue. I spend a lot of time going through the collection and removing photos and now it seems I have to start over again.
Thanks,
Antonius