I have do some "magic trick" with...upgrading Ubuntu 16 (libc6-2.23) to 18 (with libc6-2.27) and...
....progpow started to work.

there are maaaany rigs with ubuntu 16, that I cant "just like that" upgrade. Could You compile miner under ubuntu16 (with older libc6? - maybe this is problem?) or give us source code of miner?