I've just moved to RubyMine on my macOS High Sierra and I've got the exact same issue. I use RVM with Ruby 2.4.3 in my project. I've got `.ruby-version` file where my ruby is set to: ruby-2.4.3 and `.ruby-gemset` where 'caffio' is set.
I keep selecting my Ruby version but it doesn't get set. Any ideas how to fix it? I tried deleting `.idea` but it didn't help.