Idle clients

[toytown]

If I check the filesize of the backdrop images it reaches from 900kB to 7.1mB

This also kinda ties into another post i made yesterday.  Some of the backdrop images are originally stored as 2160p images at 2MB, but they are then cached on the same drive as a 12MB image (6x increase).  Not sure why jellyfin doesn't just serve the original (ever so slightly better quality and much lower sized image)?

Edit

So this could really cause the traffic over time

Yes i think you solved it, i used tcpflow to get the same data you did and i just see a bunch of backdrop requests all the time in the log. I think some logic needs to be used to stop it sending bigger files than the original backdrop though.

If the original URL request has "&quality=xx" set, then the requested can be reduced, so the logic is there in the code and could be forced by using nginx or a similiar proxy. Hopefully the devs allow it to be set in the admin dashboard in future.