Visitor graphs not working anymore

I have no idea if I found a bug, so I decided to ask here first.
Currently I am using Matomo 4 RC2 with PHP 7.4 and Nginx which is working mostly fine.
But, the graphs stopped working. I still see visitors logged, but the graphs indicated that there are no visitors. Also the statistics are empty.

Any idea? Or should I open a bug on Github as it’s an RC version?


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