woodyc

Thanks, Dazmondo77! That worked worked for me.

For any other Mojave users who have had trouble with the MAS hanging on all downloads (for me on two different macs running Mojave) I found a solution that worked from a user (User366) on stack exchange, that sorted the app store:
APP Store Fix
Go to Activity Monitor and force-kill appstoreagent process. The app started to download at once. After force-killing appstoreagent, there was no need to log out and log in again in the App Store. Updates and downloads just work again.
Hope this helps
Now have Pub Des Pho working great on both Macs - Great work team

I figured out how to resolve it.  The fix is on the macOS side.  It looks like information about the folders is cached and somewhere along the way Affinity probably misconfigured the folders (after looking through the forums, it looks like these folders at some point would both go to Affinity Photo, but that was resolved later by the developers).  Since I have been using both Affinity programs since the day they were launched, I probably had some remnants of this somewhere that was hosing my iMac and MacBook.
Steps I followed (use at your own risk):
- Go into iCloud settings and turn off Affinity Designer and Affinity Photo in the iCloud Drive settings.  This DOES NOT delete your files from iCloud.
- Go to ~/Application Support/CloudDocs/session and then delete these files and folders to the trash:
6LVTQB9699.com.seriflabs.affinitydesigner (folder)
iCloud.com.seriflabs.affinityphoto (folder)
6LVTQB9699.com.seriflabs.affinitydesigner.plist (file)
iCloud.com.seriflabs.affinityphoto.plist (file)
This DOES NOT delete your files from iCloud or impact the Affinity software or settings, it only gets rid of details related to icons and application references for the special App Library folder on your macOS.
- Reboot.
- Go into iCloud settings and turn both Affinity Designer and Photo back on.
- Launch Designer and Photo.
- Check the iCloud Drive folder and the directories should be correctly setup.
Hope this helps anyone else who has this bizarre problem.