I installed AirVPN yesterday on my laptop with windows 8.1 and have very similar problems as OP.
But the solution doesn't work since I can't end / terminate / kill openvpn.exe, not by Task Manager, nor by Process Hacker, nor by cmd. I've been googling for hours, tried to disconnect all possible devices and disabling/enabling all possible drivers. I do have OpenVPN installed as well but the GUI isn't running (and openvpn.exe wasn't running either before installing). Openvpn.exe doesn't show any sort of cpu activity. The problems started after reopening my laptop (sleep mode).
I know I've been avoiding the most relevant solution ("have you tried turning it off and on again") but I'd really like not to restart my computer as there are other programs running in which I can't save my activity.
Have I missed something obvious or is there no other solution but a clean restart and not to use sleep mode anymore? In that case I'm afraid I'll have to look for alternatives.
On a side note, yesterday I tried a couple of servers in the Netherlands, and got about 5Mb/s downloadspeed in tunnel and ~22Mb/s outside the tunnel. Upload speed was only slightly affected. Is this considered normal?