I've been pretty careful to get all the accented characters in my music tags right.
I use MP3Tag to rename based on tags, so I end up with accented characters in my file names. Windows and SB server handle these file names with accented characters just fine. Sadly, MusicIP does not - and there's no point in waiting for a new version that has this fixed.
One solution, which is working for me, is to just rename the files and folders, 'flattening' the accented chars into the non-accented versions.
I started to do this by hand - too big a job.
I then took a stab at writing a Python utility - and immediately found that Python doesn't do well with mixed Unicode and ASCII (do-able but a PITA)
Gave a bit of thought and realized that I already have a utility that can do this - Bulk Rename Utility. (free, BTW) I hadn't thought of it as I use it as a regular expression renaming tool (great for that - but regex, as well, isn't the right tool for accent removal)
Anyway, BRU has a checkbox for removing accents, and, at the bottom, you can both select through all subdirectories and use a selection criteria (like '*.flac').
So... once I figured the right tool, I was able to 'flatten' my files in about ten minutes (about 70K flac files with ~1K with accents - music is spread over a couple of drives; I did one pass for folders, another for *.flac). Did a refresh/add in MusicIP, and a 'find new' in SB server.
And now MusicIP is including the previously-excluded files in mixes.
The only downside I can figure is that I now have some CUE files that are wrong. Doesn't matter to me, but it might to you.