Did you find a solution? I have the same problem on Mac with High Sierra and a very new Affinity photo version 1.10.5.. It happens with any photo immediately when I go to the tone mapping persona. It hangs itself. Looks like it's processing something with a blue bar that says "tone map", but doesn't do anything. I have not found out, yet what tone mapping even is. I can't cancel the process, I can't shut down Affinity, I can't even restart my computer. I have to emergency restart...... Everything crashes. Also I can't find any customer support to help me with that problem.
Happy for any help!
Tanja