If your other web use software is much quicker. My guess is that your router vpn connection limits the number of active connections per task. Try this in tribler in settings under connection the ‘max connections per download’ and set it manually to 10 and test your download speed. If it does get quicker then try 25, 50 and 100 connections. If it suddenly drops off even with plenty of seeders seeding then that’s probably your problem and the solution is to set a fixed number of connections per dl.
Secondly install a torrent program like deluge and try downloading a linux distro. Deluge doesn’t use hops but it does use many connections to see if your router vpn blocks that.
If this bit of diagnostic testing doesn’t help then perhaps some one can help you with port forwarding tribler.
I had a similar problem as you for a while and after a time i found out that random isp and vpn blocks ended up messing up connection records for tribler and at times for deluge. Really anything that has many simultaneous connections for a single task, Even IDM (internet download manager). Only a few of the vpn servers let IDM work at full speed. I set the IDM download to a slower max speed and it worked and quicker (stable) download since it wasn’t being blocked.
Also it’s not unusual for tribler to drop to 5Kbytes/s or all the way to stopped then restart. It’s part of the anonymity. The point is not to panic and be patient. Some VPNs will randomly suspend (pause) the internet and shunt to another of their servers and reconnect. Since it’s a router integrated VPN you won’t see it shunt like you would if it was on your computer.
You probably also have a firewall either in system or in the router running. That’s also something to check that could be impeding tribler.
Just something to think about.