We know that Meshmixer is not always the easiest tool to use. And we also know that it has bugs. Some bugs we know about, many others we do not, because we haven't encountered them ourselves. So, if you would like to tell us about a bug, have a question, or just want to vent, you can do that right from inside Meshmixer. On the Feedback menu you will find an option to Report a Bug, as shown below.
This opens a form where you can describe your problem. If you include your email, we will try to get back to you with something: a suggestion, questions about how to reproduce your bug, or at least an apology!
Another great place to learn more about Meshmixer is on the Meshmixer Forum. There several expert users can help you with all sorts of problems.