I posted this somewhere. I may have been on the Affinity forums. In any case, if anybody Googles into this thread....
Affinity has two installers for Windows. One, which is meant for the Windows App Store, I guess, installs the program in some crazy place under the user's AppData directory. Bad things happen, including that other programs have trouble starting the Affinity product.
If you go to the Affinity site you can download the program with a normal .EXE installer that will install the program in the normal place - in Program Files - and everything will work fine, no workarounds needed.
I uninstalled the Affinity programs and reinstalled using the MSI/EXE installer. None of my preferences were destroyed and everything was chirping birds and smiles.
That said, make sure you back up your prefs and addons first, like always.
One thing to note: Starting Affinity with the Control key down will bring up a dialog for deleting your prefs when the program starts. The keystroke in Photo Mechanic for "Edit" uses, yes, the Control key. It's easy enough to click "Cancel" and not worry. Once the program is running, there will be no more of that nonsense. It's also easy to one day accidentally click to delete your prefs. So. Backup your prefs!
If you start Affinity first, so it's running when you Control+E a picture in PM, you will not see that prefs dialog.
On the Mac version, this doesn't happen. None of it, actually. So there's that.
Happy Googling
-Carl