Compatibility issues with MainStage 3.6
As posted on our website, the current 3.6 version of MainStage is not reliable - we have been recommending people not to update. For some people, 3.6 is working fine, and then for others, it does not work. It might even open a concert file fine 1 time, then crash the next! Sadly we are waiting on an update from Apple to hopefully fix some bugs. If you have a backup of an older version of MainStage, we recommend using that instead! (version 3.5.3 has been rock solid!)
As always, do not update to these newest software versions until you can verify that all of the other music software (plugins etc) and hardware (interfaces, keyboards etc) you use on a regular basis are compatible. If you do want to go ahead and try the latest MainStage version, update responsibly by having a backup of the older version - Check out our support page on this topic here.