I was also experiencing issues with Wireguard (Mullvad) on the latest version since updating, speeds were stuck at 1MiB/s maximum, a far cry from the 60 I usually get.
I rolled back to 4.4.5-1-01 using the exact same configs and now speeds are back to normal. Happy to provide more details if that helps in diagnosis.
EDIT: Also interesting to note is that it only seemed to be download speeds which were restricted, seeding speeds seemed okay. I did also try fresh openvpn configs from Mullvad on the latest version and it just wouldn't connect. I've just tried mullvad openvpn on the older build and I'm getting issues as well, but I prefer using Wireguard. Happy to provide logs on that as well if it will be helpful.