sp_BlitzWho Does Not Complete
Yeah, that's the older version. We released a new one a couple days ago that has a performance improvement for that query.

The join in the new code should look like this (as well as use a table variable (I know, I know), and also READ UNCOMMITTED):

WHERE (s.session_id = b.session_id
OR s.session_id = b.blocking_session_id)


The newer version should complete in roughly the same time as the lovely and talented sp_WhoIsActive.