@steveits Thanks for your reply. I am aware of the changes. I was initially on 2.4.5, then went to 21.02-p1, and am currently on 21.02.2.
As mentioned, the issues started after the 'upgrade' from 2.4.5. But a few details that I will add since I was thinking back:
Very rarely, the speed on transfers does go up to the expected speed of around 40 MB/s and lasts a few minutes, but then returns to the around 8 MB/s. Unfortunately didn't catch the logs when this happened.
Also, the logs look normal, just the dashboard checking the IPsec status in the normal fashion.
CPU usage does rise when Async is turned off, but speeds stay basically the same regardless.
The issue is not like what is mostly mentioned by others, where the tunnel does not stay active. Mine does stay active, and is rather stable, its just that the speed is much slower than previous, with the same settings.