Composition broken after upgrade
I have just updated to Fedora 30 from Fedora 29 and my gnome wayland session does not work any more when a second monitor is attached to my HDMI port. The problem is that the laptop monitor shows garbage (mostly black and some misplaced screen content which looks quite interlaced, as if the frame buffer was misaligned or written to an incorrect place of the memory) and only the attached one works fine.
If I unplug the monitor it usually recovers from the condition. And if I use xorg everything goes fine.
My main suspect is mutter, because it looks a lot like a video rendering problem. I first thought about the VGA driver, but given that xorg works perfectly, it looks more like a higher level issue to me.
I’m using a MacBook Pro with an “Intel Corporation Crystal Well Integrated Graphics Controller (rev 08)” VGA card. The laptop's monitor is a Retina and the external monitor is not, though the external one is physically bigger.
Also, playing with resolutions and scale factors, the problem seems to disappear for some configurations but unfortunately they are not usable because displays are too mismatched (from the real world) in sizes which makes windows/fonts unusable because of being too big or too small.
I would like to get some help on how to diagnose this problem better to make sure it is actually a bug in mutter and, in case it is, try to help as much as I can to fix it.