I got my MIST a couple of days ago and have been playing a little with it
One of the things I did was to copy in the Amiga OS3.9 disk image and custom kickstart that I built for my Minimig, and it seemed to work well, until I noticed that I did not have the amount of Fast RAM I was expecting. So I started experimenting, and it seems like the 24MB of Fast RAM easily "fall off", for reasons I do not know. Sometimes when I reset the Amiga side, the 24MB disappears, sometimes running SetPatch - even OS3.1 setpatch - makes the 24MB disappear, sometimes they disappear when the box is up and running, which of course causes the system to freeze up in glorious ways
This does seem to affect both the AGA core and the "ECS-only" core.
Am I the only one who experience this? Could it be hardware? A full reset using the power button seems to always give me back my RAM, at least from start. Selecting 4MB instead of 24MB also seems much more stable, they tend to stick around much longer.