I’d love to know if there was a solution for this. I’m having terrible slowdowns, including waiting more than 30 seconds to flip the image horizontally. This happens with files over 100 MB very often. There are also a lot of other sporadic slowdowns. In the file for which I attached info, it takes an excessively long time to select via alpha to selection. After resizing even a small selection via transform, it will take 10-15 seconds for the done button to respond.
I don’t have problems like this with Procreate or Affinity. I’m telling you that so you have that information, not to make invidious comparisons.