I spoke with online tech support and was instructed to try the following:
In the Finder, launch System Preferences and navigate to Security & Privacy > Privacy tab > Full Disk Access. Click the lock icon in the lower left, enter your admin user name & password. Click the + icon and add Lightroom and Aperture to grant access to your hard disk. DO the same for all other Adobe apps too. Then restart again and check. Do the same for both under Accessibility and Photos too in the same window. Then restart.
This didn't fix the issue. He said he need to check is resources, but after a couple of hours I figured he got lost down in the basement or something. Speaking to second guy he suggested I create a new catalogue, which I did but this also didn't work and was at a loss...
Unfortunately, Apple and Adobe didn't put much effort into making the Aperture import plugin.
One thing to try is to split your Aperture library into multiple libraries and then import each one separately. This may help you isolate the photo(s) causing the error. If one particular library still fails, then iteratively split that into smaller libraries.