https://bugs.winehq.org/show_bug.cgi?id=50079
--- Comment #2 from Hans Leidekker hans@meelstraat.net --- Does it work if you pass the full Windows path to msiexec? E.g:
WINEPREFIX=/home/wineuser/.wine su wineuser -c "wine msiexec /i z:\tmp\wine-mono-5.1.1-x86.msi && wineserver -w"