READ THIS: A possible fix if you cannot download or update Logic on Mojave
Earlier today even the renowned German tech website heise.de has reported about the recent App Store issues on Mojave. They linked to a developer's blog post with detailed analysis of the issue. The latter linked to an earlier blog post by Rob Griffiths who offered the following solution:
“
- Quit the App Store app.
- Switch [your] DNS to another provider. [may be optional if the rest doesn't help]
- In Terminal, paste this command and press Return: open "$TMPDIR/../C/com.apple.appstore/"
- Confirm that the Finder opened a window to the com.apple.appstore folder, then drag everything there to the trash.
- Back in Terminal, paste this line and press Return: killall -9 appstoreagent
- Relaunch the App Store app.
”
Haven't tried it myself yet.
Hope that helps