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.
When I click on "Locate," another dialog box appears. For example:
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.
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.