Here is a bug I stumbled upon:
When I replace an image via the "replace document" button on top, the document (an Affinity Photo file in my case) gets updated and shows up correctly in the thumbnail pages on the left. However in the central workspace the old image is shown when zoomed out. Once I zoom in the image changes to the correct one. When I zoom out it changes to the old one again.
One note on "replace document" it would be great to have a shortcut for this or/and put it also into the right click context menu.
Great job so far, this looks like it will be a great app once finished. ;)