I have had a couple dozen incidences of formmule running for the last few years and have had very little trouble. Somehow I got the heads up early on about not duplicating column names and other best practices and I guess that has paid off.
Further more I'm careful not just click the save button every time I open an existing incidence. If things are not the way I left them I double check that it's looking at the correct tab/sheet and if that doesn't work I close and reopen. Usually that fixes it.
Many people that use formmule work for school systems. If that's the case with you, the problem you're going to have finding an alternative, is finding one that has been vetted to be safe for student information.