Few days ago I wrote about troubles with Spacechem.
Customer support (GOG and the official one, probably creator himself) was polite and appeared to genuinely trying to help me with my issue. To be honest, after creators of Darkest Dungeon (Red Hook Studios) have been ignoring me for almost a year, after writing they are handing the issue to the devs, I was pleasantly surprised to read e-mails from a studio which actually cares about their players, even about those in minority, the Linux ones.
Few ideas how to solve the issue have been suggested, I have a few in my mind too. When I have some spare time I will try to resolve (work around) this issue. It was also great to hear that more recent games from Zachtronics are not using old SDL (1.2?), but either SDL 2 or Unity, so these multi-monitor issues should not be present.