sp_BlitzFirst fails when outputting values to tables
When we renamed it sp_BlitzFirst and went open source, we made several breaking changes, one of which was changing the history table's DATETIME field to be DATETIMEOFFSET instead:

https://github.com/BrentOzarULTD/SQL-Server-First-Responder-Kit/issues/288

I would use a new history table name, and then it'll get automatically created with the right datatype.