Apple Arcade Keeps Losing My Progress

I'm on a free month trial of Arcade. I'm only using it on one device: my iPhone SE, iOS 14.7. I only tried two games so far: Spire Blast and Slash Quest. After playing SQ for about 90 minutes, I launched it again and had to start from scratch. I assumed the problem was with that game, but just now I launched SB and again, starting from scratch. Weirdly, my achievements are all still there, but I'm expected to start again from stage 1, losing 100+ stages. Tried restarting my device and that's about it. I'm obviously very discouraged from trying any other games on this service because what's the point? Any tips welcome.