No Pictures displayed in backend

I added about 15 albums and inserted many images

For some reason, I uploaded 6 images yesterday
In the backend in the album I only see white space, no thumbnails
In the frontend the pictures are shown

Please help, this is annoying for in the backend I can not see which pictures are shown

Hi Stichting.
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What was the solution here, please? I am having the same issue.

Hoi Marcel. Karakters zoals ( en ) in de naam van de file

Soms helpt een andere browser

Hi Marcel,

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