Im facing the same problem as in the linked post, and it is also something to do with + and - as pressing them changes the behavior of the slice tool when in grid snapping mode. Im on 1.3.17 version on linux.
I’m sorry, I can’t reproduce the issue. If you don’t mind, could you send us your aseprite.ini to support@aseprite.org. (To locate the aseprite.ini file, go to Edit > Preferences > General > Locate configuration file)