P: Error while creating Virtual Copies

When I try to create a virtual copy in Lightroom ClassicI get the following error:

"An internal error has occurred. ?:0: attempt to index field 'additionalDevelopMetadata' (a nil value)".

The error started after I combined a second catalogue into a main catalogue using the 'Import from another catalogue' function.

The error only happens with the images from the second catalogue that have been imported into the main catalogue. All other images in the main catalogue are fine. I still have the second catalogue and the virtual copy works correctly in that catalogue as well, so the issue appears to be related to the import process. The reason for combining the two catalogues was to reduce the need to swap between the two.

I had already done quite a bit of work on the imported images before I came across the virtual copy error, so I now have a bunch of edited images in my main catalogue that won't allow VCs to be created, and a bunch of un-edited images in the old second catalogue that will allow VCs to be created.

My system details are as follows:

Lightroom Classic version: 9.1 [ 201911291132-64cf80b4 ]
License: Creative Cloud
Language setting: en
Operating system: Windows 10 - Home Premium Edition
Version: 10.0.18363
Application architecture: x64
System architecture: x64
Logical processor count: 8
Processor speed: 1.9 GHz
Built-in memory: 16192.0 MB
Real memory available to Lightroom: 16192.0 MB
Real memory used by Lightroom: 1050.7 MB (6.4%)
Virtual memory used by Lightroom: 1068.6 MB

Similar issues have been reported by other users on the following Adobe Community thread:

https://community.adobe.com/t5/lightroom-classic/error-while-creating-virtual-copies-in-lightroom-cl...