Activity Search does not allow you to search for the SQL SPID, the column is not taken into account when looking for results. It would be very important to have this information when trying to debug sql blockings. Often, the headblocker is not visible in the active queries just its victims. Main reason is, that the head blocker needs to execute something to become visible, which is not always the case.

Without the head blocker data, it is not possible to track down the actuall blocking processes activity id etc. to get more insights into what was going on.

The only workaround currently is to log onto the sql server, use sys.dm_exec_sessions to get the host process id and query that one. This will not work on production, of course, where this help would be most important!