Please include as much of the following information as you know and limit each issue to one report:
Version/revision of MuseScore you are using (e.g. version 2.1, revision 871c8c3). Check Help → About... (Mac: MuseScore → About MuseScore...).
Operating system being used (e.g. Windows 7, macOS 10.12 or Ubuntu 14.04)
If reporting a bug, describe the precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.).
If you are not able to reproduce the problem with the steps, it is probably not worth reporting it as the developers will not be able to reproduce (and solve) it either. Remember that the goal of a bug report is not only to show the problem, but to allow others to reproduce it easily.
attach the score that shows the problem —use the "File attachments" option at the bottom of the page, just above the Save and Preview buttons when you're typing your post.