I have been able to reboot via terminal and upgrade successfully.Was a .log file emailed to your set notifications email?
Usually more detailed information is in the .log file than in the event log.
A screenshot of the email you are looking for is under step 3:
https://voxtelesys.com/tutorial/debian-9-stretch-to-debian-10-buster-and-3cx-v16-to-v18
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