When i connect to my jellyfin server to stream/download video/audio the speeds are tied to my internet speed. If my internet speed drops so does the transfer rate from my server. However it seems tied to my internet download speed (which varies from 0.5 to 80 mb/s), not the upload speed(which is usually 2 mb/s), and if i disconect my router from the internet I’m able to react the maximum allowed by my hardware. Is this normal? Or maybe something is wrong, or needs special configuration?
If relevant, I connect to a tp link router, which connects to the router from my isp.
Correlation does not imply causation. It could be that the same thing that is lowering your internet speed is affecting LAN, perhaps the router not being enough to handle the traffic, or something in the network occupying a lot of bandwidth which is only active when there is internet (e.g. a download client, or worse a download client accessing a NAS).
In any case you need to give more info into what your setup looks like, e.g.