I’m not even sure if it is the avastSvc.exe which does the registration process, if it is then it could be the C:\Program Files\AVAST Software\Avast\Setup\setup.log file. But that can be quite large and not very user friendly.

Though if you initiate the registration again (make not of the time) and look in the setup.log for that time frame (the log in in oldest first, newest last), it should be close to the bottom of the file. You could copy and paste the last 100-200 lines.