I guess I've created Frankenstein LOL. After a day of reinstalling everything, formatting ssd, changing batch files etc I gave up and thought it's a hardware issue - after all motherboard in this rig is almost 12 years old. So I went ahead and ordered new MB+CPU+RAM, thanks to BTC hitting new ATH that day. But yesterday I thought I'd give it another try. I have an image of HiveOS on one of my SSDs so I took it and installed AM and ETHpill on top. Surprise - it works! So my guess it after I installed Ubuntu server 18.04 it automatically downloaded some sort of new update which conflicts with AM. I have no other logical explanation of this issue. Testing Hive+AM for almost 12 hours now, so far so good. I guess I could've downloaded another version of raw Linux/Ubuntu/Debian and it'd work too, but I used what I already had.