I am constantly running into an issue where Emacs completely freezes when using swift-mode. I am not sure what the reasons are, or how to reproduce it consistently, as it seems to be somewhat random while I edit swift files. However, I've identified where it is happening.

In the function swift-mode:syntax-propertize:scan, this part

Moves the point back to the start of the match, then the function (forward-comment 1) is called, expecting the point to move to the end of the comment. For whatever reason, the point doesn't actually move, so that (point) is equal to start, resulting in an infinite loop.