Frigate Addon over nginx proxy extrem slow

I have home assistant installed on an Intel NUC as supervised running frigate as Addon. On local network I can download frigate exports with 1Gbit speed, so it is very fast. I also have no speed issues with home assistant.

But if I open home assistant and frigate over nginx proxy manager, no matter if from internal network or over internet it gets really slow, something around 50kb/s max, I see this when trying to download the frigate export.

Why is it getting that slow? Is there any setting I miss in home assistant, frigate or nginx? Does anyone know why I have this problem?