This may not actually be solvable.

The problem here is inferring when the class definition ends in general (especially when you don't have an open curly brace) is based on a complex series of rules, most notably including a double newline. This is the same set of rules that applies to other type definitions. The issue in your example is there is a double newline, it's just hidden by the comment. Scala reasonably considers the comment line to be "not blank", but it's harder for Sublime to make the same judgement.

I would definitely like to fix this, but I'm somewhat skeptical that it's in the cards.