P: Message: "The catalog could not be opened due to an unexpected error."

This thread is being merged into an existing authoritative thread for better tracking and response. Please review the official answer (if any) in the second post on the thread for more information. 

We need some additional info to investigate this further.
I have sent you a mail with details.

Thanks,
Sunil

I'm sorry Adobe but over the last 12 months every time there's an update there seems to be a problem.  If it's not Media Encoder then it's Lightroom Classic.  There was a similar issue to this in December and then a new update resolved that problem and now it seems similar is happening again.

@JPEG same thing happens to me

same thing happening to me! Im using a Mac are you?

When I update Lr classic this error “ Unexpected error opening catalog; choose a different catalog, try again, quit” happens.  Anyone have any ideas how to fix this? My Mac needs to be updated to Big Sur 11.2.3 (I was waiting for the next version to update). Lr works fine when I go back a version. I called support and tried their chat and it was a waste of time. I have a Mac using Big Sur. 

After ~16 hours (overnight) with no other usage of this computer, the catalog opened on the first try. "Integrity check" message box popped up briefly. (March 23)

My iMac is not showing any other kind of odd behavior.

Could this be related to some Adobe cloud/sync intermittent issue? When this fails, is my LrC 10.2 instance reaching out to some online Adobe service that it cannot find?

Failed again (March 22).

I successfully opened it 2-3 times as a test, then it failed again today.

Same error dialog:

I reported this also to @8510810 there are too many reports now for this to be a hardware error

Me too!  Reminiscent of October in that booting usually results in the catalog opening on the first try but not subsequent tries.