I was using several VPN connections for quite a while now. At least 2 years (it could work before that, i just didn't have to use more than one vpn before)

Were you connecting to them at the same time? That has never worked for me (the first one gets disconnected when I connect the second). I had to use Gopenvpn for that.

Yes. In fact I am using it right now. What I suspect your VPN fails routing. When using more than one VPN you need to be sure to have proper routing for each. In my case it was a matter of checking "Use only for resources on this network" on IPv4 Routes page.