Odd result with tools > slash notation

Attachment missing?

Also, which menu item do you mean - Fill With Slashes or Toggle Rhythmic Slash Notation? The former needs the measures are currently empty, if they aren't, it will try voice 2 then voice 3 etc until it finds an empty voice to place the slashes in. So if that is what you are trying, then presumably you are seeing double slashes - vocie 1 and voice 2 for every beat. Instead, you should press Delete to clear the old manually-create slashes before filling with the new slashes.

For "Toggle Rhythmic Slash Notation", I don't think you'd normally expect to see anything happen if the notates already had their heads turned into slashes manually. But they will now become "true" rhythmic slash slash notation - immune to transposition, silent on playback. If they were stemless before, they will remain stemless.