P: When trying to add files to Collections I get this error: ?:0: attempt to compare two nil values

Thanks. This ist working with the target collection. I have only sorted the original collection first.

*naturephoto_kk 

As John Ellis said:

See the workaround at the top of this thread:

https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-classic-when-trying-to-add-files-to-collections-i-get-this-error-0-attempt-to-compare-two-nil-values/5f9091ea35f40c2520b9ecc4

Same error here with my Lightroom 10.

As John Ellis said:

See the workaround at the top of this thread:

https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-classic-when-trying-to-add-files-to-collections-i-get-this-error-0-attempt-to-compare-two-nil-values/5f9091ea35f40c2520b9ecc4

I'm getting just the same error message when I try to move images to some collections -  but so far mercifully not to all. It's a damn nuisance - when will they fix it? Also, I've had a couple of unexpected unwanted shutdowns.

See the workaround at the top of this thread:

https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-classic-when-trying-to-add-files-to-collections-i-get-this-error-0-attempt-to-compare-two-nil-values/5f9091ea35f40c2520b9ecc4

Why conversations get merged: https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-auto-import-to-folders-organized-by-date/5f5f44f14b561a3d422ab0ba?commentId=5f5f48984b561a3d422bdf45

What collections?

Please post a screeen shot of what you are seeing on your system.

A workaround that's helped several so far: Select the problem collection and do View > Sort to change its sort order to something other than Custom Order.

Very useful mitigation. Should be highlighted at the top. Thanks.