I'm having the same trouble with the Mac Version. I'm currently trying to average an image stack of about 70 frames. Loading the frames into Affinity Photo took all night, it shows the small previews of each stacked layer, but I cannot see an image on the main viewer. Trying to export the result is currently running at 4h, but I have to break it off since I need the computer for something else. Looking at the Activity Monitor, it uses about 25GB of RAM (which is ok for that amount of full size layers), and an insignificant amount of CPU usage is registered (well below 100%).
Even smaller projects take forever to export (minutes). It is mostly easier to just take a screenshot of the result than to save an image properly, if I do not need full resolution files.
I'm working on the older Mac Pro with 32 GB RAM and dual graphics cards.
