So guys, finally found the problem: the new behaviour of Eddie to look for .ovpn conf files in /ovpn just below the data dir obviously makes it difficult for him to find the respective key- and certfiles. I did a little debugging with procmon in Windows and after I changed the relative directives in my .ovpn conf to something like that:
ca "c:\\myvpnserver2017.crt"
cert "c:\\myvpnserver.crt"
key "c:\\myvpnserver.key"
it finally works. Maybe this is a helpful note to fix this bug ...