Photo's are not syncing due to "invalid modification date"

My photo’s have stopped syncing and I only realised it today. Apparently, one or more files have an invalid modification date. I have tried to track them down and some files indeed had meta data that indicated they were taken in 2109. Probably a corruption during sync. However, It still does not work and the nextcloud desktop client does not specify what the problematic files are. Can anyone help me? All online tutorials work from the premise that you have access to your Nextcloud server.

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Having the same problem on my Windows 10 computer. A specific folder containing photos is affected. Reinstalling nextcloud did not help.