Affinity Publisher Beta 1.9.0.822 - MacOS 10.15.7 MacBook Pro
I created a vertical stack of five small identical picture frames and dragged to select them all.
Chose Alignment > Space Vertically which worked, but instead of clicking Apply I just clicked back on the document. This immediately crashed Publisher. I repeated this several times. Clicking Apply works just fine.
Moral of the story - Use the app as it is designed and it works but don't go clicking where you're not supposed to. 🙂
Geoff