In my experience the best way to get reply from devs nowadays is to contact them via chat on discord whenever they offer a discord chanel. Luckily in this case there is one:
https://discord.gg/t5YqxDG It's possible that the devs updated the basegame without updating the DLC so maybe they are simply incompatible now. It also might just be a GOG specific issue. Anyway it would be a good idea to tell the devs about it.
Actual Steam version is at 1.1.104 and GOG is at 1.1.104 as well - so it's not a missing base game update in this case.
According to GOGdb (I don't own the DLC) the shop DLC has been updated to 1.1.104 as well. Seems to be a GOG related issue.