There is definately a bug with the Mac App Store on Mojave 10.14.6
I tried downloading the updates to Affinity Photo, Designer and Publisher yesterday almost as soon as they were available.
The updates seemed to be hanging - even after around 30 minutes so I decided to quit Mac App Store and try again today.
However, today when I launched the MAS my Affinity products weren't available to update - only to download (even though they are already installed).
I then killed the "appstoreagent" task and relaunched MAS.
I'm now seeing all three Affinity apps available to update but once again the update process seems to be hanging.
This is very frustrating! I've never had this issue before with updating apps before...