Very slow Gateway connection

I’ve been struggling with this issue for days. I couldn’t get more than 1mbit bandwidth using Whonix Gateway, most of the time even less, about 300kbps. I had this issue on my desktop PC but not in my laptop, using the same connection, at the same time, and connected to the same router.

I generally download and install a fresh VM whenever a new version of Whonix is released. As I installed version 9.4, I started noticing this performance drop, but I thought it could be normal, something related to Tor network itself. But then it became unacceptable, like I said, 300kbps average.

So, I installed a fresh copy of both Gateway and Workstation 9.6. The problem persisted.
I thought It might be something wrong with my desktop PC (as my laptop was doing OK), and tried a lot of things, with no luck.

Finally, I copied the Gateway’s virtual HD (version 9.0) from my laptop and attached it to the desktop VM. Voila. 5mbs average.

I have no idea what the problem could be. A Gateway bug? A Tor bug?
Either way, I think I’ll have to keep this outdated Gateway for a while.
Any thoughts?