I am having this same issue iPad Pro 2018 OS 15.02 Affinity Designer 1.10.2 (i tried on my iPad mini OS 15.02 -AD 10.1.2 ) and it did the same thing eventually.
For me it occurs when I am dragging an object up or down in my layers studio. Much like this last user mentions the app just disappears and does not save any of my last iterations. This did not occur until this last update. I don’t have a video but I have seen it enough times that I have narrowed it down to moving objects within the layer studio. (ie. Tap hold and drag a curve or object up or down in the layers studio and this is when it will intermittently crash on me).thank you for looking into this.