I travelled to Scunthorpe today and again there was a single 185 in use, the 1418 Manchester - Cleethorpes was a single set, not good for a Saturday afternoon!
You do seem to have rotten luck. That set was a single because 1B96 (22:20 MAN-DON) the previous day was stuck behind a failed freight train in Cowburn Tunnel. The train was delayed so significantly that it had to terminate at Sheffield and stable there overnight - the driver was out of hours to continue to Crofton Depot.
As a result Crofton were a unit down for the next day's service, hence the shortform on the diagram forming the 14:18. With the drivers that were available, and to balance the units and get things set up correctly for the next day, there was no opportunity to restrengthen the diagram in time for the 14:18.
Very unfortunate but just goes to show how significant a knock-on impact some of these things can have.
Most likely resulting from units trapped in Hull due to engineering blockade (Micklefield to Selby) which are required for service first thing on Monday morning that can’t rotate
Nope, got nothing to do with that. If there's a block on between Leeds and Selby, there will simply be a few units sitting idle at Hull. It has no significant effect on rotation.