Matchmaking doesn't work Mac to Mac?

For some reason, when I create a build for my game, playing between a PC and a Mac seems to connect fine. The game doesn’t have any issues.
But when playing between two Macs, there are significant issues. Often the game doesn’t work at all, sometimes it runs for a minute and crashes. Why is this?

We’re not aware of any such issues. I’ve just verified this using our demo projects on version 5.2.1 (latest) between two mac machines. Maybe there is some information in the log files? If you can narrow it down to a simple scene with repro steps I can have a look at it (just submit bug with info and PM me the case number).