After opening a saved Prism file, some sheet names have changed.

We only know of one situation where this happens. 

1. Create a project in Prism 5 (windows or mac), and include a slash (/) in a sheet name.
2. Save in .PZFX format
3. Reopen the file.
4. You'll see that the slash symbol, and a few adjacent characters are gone.

The workarounds are simple: Either avoid using slash symbols in sheet names, or save files in PZF (rather than PZFX) format. This is fixed in Prism 6 Windows. Prism 6 Mac won't remove any other characters, but slashes (and some other punctuation) are removed from sheet names.