Hmm, can't even turn the crank = really seized up! Would lean more towards crank bearings now, but don't believe the nub/stopper could have caused all of this unless maybe it somehow got sucked in and blocked a passage...? This is what I am personally hoping for, as this might force Ford to get-off-their-asses and redesign the anti-drainback rubber stopper in the oil cooler in this engine.
The older brother of this engine (JLR version) is known for crankshaft failures so that is also a possibility, even though they hardened the crankshaft in the F150 version of the engine.
You indicated you handle all of your own oil changes and use the F150 Diesel Oil (WSS-M2C214-B1 Specification)
- Which F150 Diesel Motor Oil are you using?
- SAE 5W-30 F150 Full Synthetic Diesel Motor Oil (XO5W30QFA)
- SAE 10W-30 F150 Diesel Motor Oil (XO10W30QFA)
- Did you add all 6.5 US quarts?
- Did you check dip stick after fill?
By no means questioning your DIY abilities or experience but rather trying to get to the bottom of your engine failure, because this is a first we have heard of (not caused by the 18E02 or 20E04 EGR By-Pass Valve recalls) and you definitely have the attention of everyone here!
My personal opinion is that you did nothing wrong and this is a one-off catastrophic failure caused by loss of bottom-end lubrication (reasons unknown) w/top-end piston & valve damage being collateral damage from the bottom-end locking up at 80 MPH.
Good to hear that Ford is sending a new engine and installing free-of-charge under warranty.
Please keep us posted.