I have been trying to debug the same problem for the last few days.
I have a Draytek router, connecting via a Windows 7 PC, I have switched to TCP 443 in Eddie, I've disabled DDOS protection, firewall, and internal VPNs on the router, and I still get the exact described problem.
Any time I try to use AirVPN from pretty much any server, it's like the act of traffic passing through nukes the connection. A brief spike of traffic, followed by 0 kb/s then recovery a few seconds later. Websites will load in stutters, games will work then completely freeze then repeat that, it's quite frustrating. Eddie's logs show nothing untoward.
I've attached a screenshot of pinging google.co.uk. The massive ping time increases are whenever I actually try to use the connection. NetLimiter tells me that I'm not even hitting 1MB/s.
PingPlotter interprets the problem as significant local packet loss (i.e. from the 10.4.X.X location onwards).
Any insights others can share as to further debug these things would be greatly appreciated.
Edit: I should of course also add that without AirVPN, the connection is perfectly fine, and a work VPN works similarly without issue, so something is up specifically with how AirVPN and my PC/network environment is mixing.