Multiline input, HeaderLine: Delimit each message at each instance of Username

I have a Graylog NXLog configuration that contains a multiline input. I'm trying to figure out what the best regex would be for the HeaderLine to delimit each message as a group for each instance of a username that appears in the log.

This is the desired output:

AskedNovember 2, 2019 - 1:05am