I've been using Lightroom for many years, and I've never experienced this problem until the last two updates to the application.
When I upload photos to Lightroom, the app creates a folder that is by default named with the date, in this format: 20210403.
I usually rename the folder, in Lightroom, with something more descriptive, just after the upload is complete. For example, 20210403_family-gathering.
Starting with the previous version of Lightroom, after I perform this action, Lightroom loses the connection with the files in the newly renamed folder. A question mark appears on the folder in the Navigation panel, and in Loupe view, every photo now displays a small exclamation mark in its upper right corner.
When I click on an exclamation mark, a dialog box appears, like the first one of three that I've uploaded.
The first file, which is highlighted, is the one that is missing (although at this point, Lightroom has lost track of all of the files in the renamed folder). When I click the "Select" button, this dialog box appears:
Lightroom is obviously confused, and the only way around this, in the current version of Lightroom, is to quit the application and re-launch Lightroom. After I relaunch Lightroom, it re-finds the files and the exclamation marks are gone. When I quit Lightroom after renaming the folder from the most recent upload, I back up the catalog. I don't know if this is necessary, but I back up the catalog whenever I quit Lightroom.
This is a bug, which never existed for me, until the last two updates of the app.
Greetings, The Max 2021 Photography products updates have been released and include remedies for this topic. The updates will be rolling out worldwide, October 26 and 27, 2021. If you do not see the updates in your Creative Cloud Desktop app, you can refresh the apps to see if the updates are available in your region. The keyboard shortcut to refresh is [Cmd/Ctrl] + [Opt/Alt] + [ R ]. Note: iOS and Android updates may take up to a week to appear in your App Store. Thank you for your pat...
I am moving this back to in-progress and have advised the team the fix did not work for everyone. The Classic Team has requested a new bug which we have written. Some of them may reach out to you for additional information. Thanks for continuing to update us.