I can't seem to download or update any apps purchased in the Mac App Store. So far I've tried most of the usual troubleshooting tips found by googling the issue (deleting caches & preferences, signing out & back in, rebooting). Nothing's helped at this point. I've deleted the app from the Applications folder to try to re-install it but when I click Install, the wheel on the top left just spins for a few seconds then nothing happens & the install button reappears. I don't have any problems on a different Mac. I do have the same issue if I create another account on this Mac, so it must be a system setting somewhere...
I'm not sure why this worked, but I just downloaded the apps through the app store on a different Mac, then copied them over to the problematic Mac. Since then, there have been other updates applied with no problem. I'm not sure what the problem here was.