Hi, Sorry for late response. My device has 16Gb RAM so I don't think that is the issue. I have tried what you suggested above (remove, reboot, close apps, re-install) but still get the same error. I monitored my RAM usage throughout the entire process and it barely exceeded 4.5Gb.
I purchased Affinity Photo through the Microsoft App store, and although it has installed ok, I get an error when I launch the app. My suspicion, from the error, is that the executable file path is too long, but I can't find a way around it.