Going back to 4.3.9 from October 2021 seems a bit absurd because that is SO old. I can believe a recent update could be the problem (it is currently 4.6.4) but there is no reason to go back THAT far! I have been nagged forever about the security value in keeping software UPDATED, particularly anything that uses the Internet. (I don't think I need to update Avidemux.)
Most software I now have set to auto-update because I know from experience that I am too lazy to do it manually with any frequency. Of course I CAN NOT update eMule, but I guess malware doesn't afflict that?
I have suspicions of ISP auto-throttling just because I am naturally suspicious. (Or "paradoid" as I said earlier.) I had wondered if changing a port setting might help! I do remember that I specifically set a forwarded port for the torrent to work with my VPN, and for the torrent client to stop entirely if the VPN is shut off. It worked fine for quite some time after that change. I have not made those same settings on the new torrent client yet, because I have to look up how I did it! I suspect it SHOULD run more efficiently with a forwarded port.
In my old qbittorrent I also have the "Use UPnP/NAT-pmp forwarding from my router" setting clicked ON. I wonder if I should UNclick it because the port forwarding is actually from my VPN? It wasn't a problem before.
I made sure the firewall exceptions were correct, although usually that is something set correctly during software installation.
I was getting low speeds from new YTS torrents with dozens of Seeders, which typically take 10 minutes to less than an hour to download. I KNEW something was wrong when they were crippled with speeds that made them take DAYS.
Right now I am using uTorrent because it is working, although the first thing I did was look up how to remove the noxious video advertising. When I have time I will go back and play with qBittorrent to see if I can bring it back ... to ... speed.
An 
