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

I have also recently installed LrC 10 on my PC and found that when I went to add images to a target collection or just drag and drop into a collection, I get the following message, An internal error has occurred: ?:0: attempt to compare two nil values. This is really frustrating me as I'm not a computer buff and therefore I thank you for any help. I understand from earlier post that Adobe are aware of this issue and working on a fix?

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]

By accident, I found a fix to this problem. I delete all the images in the Quick Collection. Then turned on another collection to be the targeted collection and then right-clicked on the Quick Collection to set it again as the target collection. Now the B puts selected images into the Quick Collection

occurs when pushing "B" to move a photo to the quick collection. Running Lightroom classic 10.0

Just upgraded to LR 10 and started getting this error. Here's my data:

Lightroom Classic version: 10.0 [ 202010011851-ef6045e0 ]
License: Creative Cloud
Language setting: en-US
Operating system: Mac OS 10
Version: 10.15.7 [19H2]
Application architecture: x64
Logical processor count: 8
Processor speed: 2.9 GHz
SqLite Version: 3.30.1
Built-in memory: 16,384.0 MB
Real memory available to Lightroom: 16,384.0 MB
Real memory used by Lightroom: 5,257.3 MB (32.0%)
Virtual memory used by Lightroom: 16,095.4 MB
Memory cache size: 1,103.6MB
Internal Camera Raw version: 13.0 [ 610 ]
Maximum thread count used by Camera Raw: 5
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Camera Raw virtual memory: 546MB / 8191MB (6%)
Camera Raw real memory: 553MB / 16384MB (3%)
Displays: 1) 3360x2100

Graphics Processor Info: 
Metal: AMD Radeon Pro 460

Application folder: /Applications/Adobe Lightroom Classic
Library Path: /Volumes/OWC BACKUP/LightroomCatalogs/LightroomCatalog-OWCBU-v10.lrcat
Settings Folder: /Users/jamesparker/Library/Application Support/Adobe/Lightroom

Installed Plugins: 
1) AdobeStock
2) Aperture/iPhoto Importer Plug-in
3) Aurora HDR
4) DxO PhotoLab 4
5) DxO PhotoLab 4 Importer
6) Envira
7) Export to Photomatix Pro
8) Facebook
9) Flickr
10) HDR Efex Pro 2
11) Helicon Focus Export
12) Imagely
13) jf Zenfolio
14) Luminar 3
15) Luminar 4
16) Luminar Flex
17) Nikon Tether Plugin
18) ON1 Photo RAW 2019
19) ON1 Resize 10
20) ON1 Resize 2019
21) Photolemur 3

I have the problem too, changing the order isn't working for me either. 

A Quick Collection fix that worked for me.  Like others, any attempt to add an item to the quick collection with a B or clicking the little dot at the top right of the image resulted in the error described above.  Changing the order of the collection did not work.  I opened my quick collection and saved all images as a new collection so I would have my picks.  Then I removed all items from the quick collection.  I went back to my original problem collection and was able to add to the Quick Collection with no issues.   

I'm having same problem after installation of Big Sur

I have same problem after moving to Big Sur

I'm getting this error message when trying to add an image to the quick collection. I used it yesterday and it was working fine. I tried to remove and import the image again but got the same error. 

Just today, whenever I try to drag photos into a collection, I get the error  "An internal error has occurred: ?:0: attempt to compare two nil values".

It was working fine half an hour ago, I'd added about 20 photos to the collection, and then it just suddenly stopped working. Eventually, I realised that the problem was with one specific collection, and tried deleting and recreating the collection, which fixed the problem. Just leaving this here in case anyone else has the same problem....

(Lightroom Classic 10.0, Build 202010011851-ef6045e0)

this bug seems to disappear when the order the pictures in the grid is NOT "personalised"

I also installed LrC 10 on my MacBook Pro (Retina, Mid 2015, macOS Mojave 10.14.6) a couple of days ago and I get the same error "?:0: attempt to compare two nil values", but on two completely different occasions:

1.  if I want to add an image to my quick collection. Grid sort changing does not help in my case. 

2. if I work on images stored on my NAS (WD My Cloud EX2 Ultra): Here, it is really bad, I get the error all the time if developing my images. 

Did anyone have the same problem when working on an NAS, too? Any help is highly appreciated!

I experienced the same problem, specifically dragging images to  a Gallery in the SmugMug LR  Classic Plugin. It was recommended that the problem could be fixed by going to Library>View>Sort> Ustinov Order, and change the order. For me it did not work, so I eventually deleted the Gallery, a d reloaded it with success. This has occurred twice, and each time the workaround worked.

Where my problem started was when I deleted some images in the Gallery, and subsequently reloaded them after running the Dng images through the DXO PhotoLab V 4. LR Classic Plugin.

Adobe Support told me that this is a known issue that is being worked upon.

I hope this helps.

Adrian T.

Extremely frustrating for this not to be working.   Please fix the bug.