large squares follow the brush strokes

[srg]

Large squares appear when trying to dodge. See screen recording.

Similar problem was present in older version of AP.

 

[lepr]

That's Affinity's tiled rendering being revealed by the rendering of a changed tile in two passes - a fast half resolution pass then a slower full resolution pass.

You can prevent the flickering by switching to one-pass rendering in the Performance controls of the app's preferences/settings.

Change the Retina Rendering from 'Automatic (Best)' to 'High Quality (Slowest)' and then relaunch the app. ('Low Quality (Fastest)' will also prevent the flickering but the document view will be rendered at half resolution.)