Motion 5.5 spinning beach ball

I've just installed Motion 5.5 on my new Mac Mini (2018) and as soon as I hit 'Continue' at the "What's New in Motion" screen I get the spinning beach ball. Motion goes no further than the "What's New" screen.

Here's what I've done so far, with no success:

1. rebooted
2. uninstalled / rebooted / reinstalled Motion
3. restarted Motion with Option+Command to reset preferences
4. Cleared the NVRAM
5. Boot in Safe Mode (Motion won't work in Safe Mode)
6. Disconnected all none essential devices and repeated all previous steps

Mac Mini (2018)

3.2Ghz 6-Core Intel Core i7

32Gb RAM

Intel UHD Graphics 630 1536 MB

I can't attach the log file as it's too big.

Any help would be greatly appreciated.