at Brickfrog’s suggestion I crossposted this on the piracy community, and someone did incur in the same issue. Apparently it’s a ProtonVPN DDOS protection, and the fix is lowering the number of max connections, so you’re kind of right, though it’s server-side. I’m now on 20 max global connections and it seems to chug along, for the time being. Now, as to why Transmission worked with 200 max connections, while qBit gets a connection timeout with 150 max, I don’t really know. Though I tried Transmission “as is” without even configuring ports, so that probably lowers the actual number of connections it can establish? I did see lower upload speeds in it, compared to my actual bandwidth and to what I used to see in qBit