Started happening to me today. I'm on 10.14.6
I noticed an update in System Preferences --> Software Update. I ignore the Catalina upgrade but underneath it said "Supplemental Update" so I agreed and installed it. I come back to my laptop and Catalina is downloaded and ready to install. I clicked nothing of the sort and auto macOS updates are disabled. I closed the Catalina installer and deleted it.
Next thing I know, when I had two app updates using the App Store, they won't update. Same error as original post here except "purchase" is replaced with "update"
I deleted the app (CardHop) and tried to download it from the App Store. Same error, now the word "Purchase" is written.
I signed out of the App Store. Restarted the computer. Flushed DNS. Signed back in, same problem with any app I try to download or update.
When I go to System Information and check Software installations, I see the installed update but no title or version information listed as is visible in other updates.
This is the kind of stuff which really makes me believe Apple is sabotaging any operating system but the current one.
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