As soon as I open Potplayer 1.7.13622, 64bit, all network traffic to and from my torrent client Deluge (v1.3.15) stops.
Meanwhile, online speed tests checks out just fine.
Closing Potplayer, Deluge is up to speed again.
Doesn't happen with VLC.
What could possibly cause this weird behaviour?
Running win10, 10.0.16299.547

Potplayer can not affect the network traffic of other programs
so
check Deluge settings - Bandwidth

Well it does.
I got everything at max in Deluge. No limitations. Right now downloading 12Mbyte per second.
Starting Potplayer, boom, instantly down to zero. Only the other background networking stuff working.
Then closing Potplayer, up to speed again.

Here's a screenshot of Glasswire monitoring the network. Yellow is download traffic. I start Potplayer, it dips. I close Potplayer, it rises again. Every time the same.
http://madmodders.se/temp/screenshots/g ... deluge.png

I have no problem with this.
I installed client Deluge (v1.3.15) and Potplayer 1.7.13622, 64bit
I tested your situation
there were no network traffic stops.

Check Deluge settings, or system.

Yeah, this is very strange.
There are no network settings in Potplayer. I thought there might be some sort of explicit access to the network card or something, like some drivers can have for power saving stuff. But no.
And there is nothing in Deluge that I can see. Nothing I change makes any difference.
I tried to set Potplayer to a lower process priority, and deluge to higher, but it made no difference.
These are the only two programs that clash with each other.
I blocked Potplayer completely in my firewall. No difference. So it's something higher in the Windows environment that interferes.
Potplayer takes about 5% CPU when playing a 1080p movie.
Oh well. I'll use another player while using Deluge, until I find out what's going on.
Out of a handfull tested players, this is the only one this happens with.

Weird. Try to use different port in Deluge, perhaps it's a conflict.