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

Your suggested workaround worked for me. Thanks very much John_R_Ellis

This thread is about errors when trying to use Sort: Custom Order for collections and folders in LR 10.   

Are the sorting issues only related to collections in the latest version of Lightroom?  I have tried to reproduce my previous sorting issues without success - but I'm not using collections in the attempts.

It looks like there are at least two different (though similar) error messages produced by the same underlying problem.

Thank you, John. I searched for my error and did not find any match whatsoever. Glad my report has found the proper home.

The text on the initial post does not list the proper or exact error code.

The entire reason for my collection is to have a custom order of photos from multiple folders. Hoping this gets resolved quickly.

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

I have also deleted the collection and recreated. Nothing seemed to help. But I did have one step that I didn't mention that may be the cause:

Did not work:

1. Create the collection.

2. Added an overview logo slide from one of my other collection folders. That is the "1" photo in the folder.

3. Set the sort order to custom

4. Attempt to add other photos. Get the error.

Worked:

1. Delete the collection. 

2. Set the sort order to Custom.

3. Add the photos to this collection

4. Add the logo and move to the front.

I can repeat this process and get the same error.

I have tried optimizing the database and restarting Lightroom. Nothing has fixed this issue. I cannot add these photos to my collection.

I use this collection to present photos from different folders together for my photography club competition. I've been doing this same operation for years. It appears there is some sort of error with the updated Lightroom.

I have just upgraded my Lightroom Classic catalog to version 10. I synchronized my library folders and added a new batch of photos. Corrected the metadata, and [CTRL] S to save that back to the files.

Next, I created a Collection to hold these new photos and attempted to add some pictures into this collection. Lightroom won't allow me to add, and is prompting:  [Error] An internal error has occurred: ?:0: attempt to compare nil with string. [OK]