Thanks Mhertz. I tried about 15 different countries: EU, my own, US, etc. No luck though.

Deluge used to work fine with the same VPN. However, since a few weeks, the following happens. Whenever I start Deluge, initially it downloads very fast - up to 1 MiB/s. Then after a few seconds, it gradually slows down to max 30 KiB/s and stays there. Meanwhile, my entire Internet connection slows ...