On a quick inspection I'd say it's because the criteria for numbers matches but without the dashes, you have spaces instead.  But t's a bit of a guess because using this alone may not be representative of what you have in the sdlxliff or what Studio may be doing (it's always possible Studio is simply wrong and it's not your rule at all):

F754 8 cm Pfoster

If you can share the file, at least with that segment in it, I'm happy to take a look?

On a quick inspection I'd say it's because the criteria for numbers matches but without the dashes, you have spaces instead.  But t's a bit of a guess because using this alone may not be representative of what you have in the sdlxliff or what Studio may be doing (it's always possible Studio is simply wrong and it's not your rule at all):

F754 8 cm Pfoster

If you can share the file, at least with that segment in it, I'm happy to take a look?

Paul Filkin

I sent you the file by email.

Daniel

The Unicode \p{Zs} and \p{Pd} character classes for space separators and dashes, respectively, can be used to avoid the need to write a list of Unicode characters.