There are a lot of optimizations in b10, so I would give that a try, first with the downgraded version of Lightroom Classic (v13.4) and then you can try upgrading Lightroom Classic. Make sure your catalog is optimized.
Hmm, that’s odd. I haven’t seen that error.
My first thought is that this could be an issue with the specific version of Lightroom you have… so first, I would try updating to Lightroom Classic 13.4.
Then, I would try the latest beta linked on the v3.1 page.
If that doesn’t solve it, I would try resetting your Lightroom preferences, then reinstalling the beta and trying again.
If that still doesn’t solve it, we can try some additional troubleshooting.
Just be aware that if you are making large numbers of virtual copies, it takes Lightroom a long time to update this in the their catalog. You need to wait until Lightroom has finished rendering the virtual copies before opening Negative Lab Pro on those virtual copies. It’s also a good idea to make sure that all the settings have been brought over appropriately (especially white balance)… I’ve run into issues a few times with making large virtual copies where some of the settings didn’t come over properly, which can result in this sort of issue.
But I will take a look at the files and see if I notice any issues…