Steam achievments not showing, either new or old ones

https://www.gog.com/forum/general_beta_gog_galaxy_2.0/steam_achievments

It's been broken for a few weeks now.

It behaves weirdly. For example 'Lines X' and 'Hexcells Infinite' were previously at 100% but went to 0% and 86% now. Samorost 2 I played and it updated until 69% and then stopped even though on Steam I got it to 100%. But the latest game I played Shadow of Mordor updates correctly according to Steam.

I even tried the plugin cache deletion and re-connection according to this workaround. But nothing helped, the wrongly updated games are still wrong...