I saw 4 green 737 fuselages on their rail carriages near Renton last week
Boeing doesn't handle unforeseen events well. It's likely that some of the workforce has been diverted from scheduled work to out of sequence tasks on the unfinished planes as parts trickle in. It's also possible that they have run out of parking spaces for engineless planes on the flight line and are holding up these fuselages.
When I worked there, I was involved with a system that delivered engineering functional tests to the shop floor. We built it so any test was available any time. Just in case a job slid in the schedule. The replacement for that system provided little of that functionality. "Plan for success" was the mantra and anything that didn't conform to the normal schedule was insanely difficult to access (managers' logins, special approvals, etc.). I fear that delays due to external causes will result in the Renton shop floor beginning to resemble a Chinese fire drill (apologies for the possible racist connotations of that remark).