I laid out a Rossini score that starts in 4/4, switches to 6/8, then back to 4/4. When I play it back, when it gets to the second or third part, the playback is syncopated, although the parts are steady eighths. Reloading the file or restarting the program has no impact. I have the current version of Musescore. I opened a new file, then copy-pasted the music to the new file, and the new file worked fine.