SQL Server 2016 SP 1 on HP 3PAR environment causes weird head blocker
When you're troubleshooting a blocking chain happening live, start with sp_WhoIsActive:

sp_WhoIsActive @get_locks = 1


There's a blocked-by column that shows you who's blocking who. The lead blocker won't have anyone in their blocked-by column.

Once you've found the lead blocker, click on the locks column - it's an XML field that expands to show you the full list of locks held by that session.

It could be that the select is part of a longer transaction (there's also an open transactions column), or that the select isn't really what's blocking.

Your best bet for getting specific, actionable advice here would be to post a picture of the sp_WhoIsActive output, including the blocking columns, and then the contents of the XML for the locks.