Hello - I came on to report this as well: 220.127.116.114 crashes when I try to brush over a mask.
Some more details: I've got about 30 layers, each with a layer mask. Whenever I try to brush the mask, the program freezes and I need to restart it. It's happened three times.
I am running Windows 10 and I have fontbase open. I've never had any issues with Affinity software before this (I've used photo and designer since last November).
I can share the doc if you need it, but it seems you've already the solution on the way. My follow-up question: where's the newest beta? When I look for the beta mentioned above, I'm only seeing the 18.104.22.1684 option. Maybe I am looking in the wrong place?