I, too, got SSSS'd yesterday Europe-EWR. First flight on a partner was fine but they never produced BPs for my onward flights on UA - through the app or at the airport. Odd. Got to my connection point in Europe and had to exit the airport secure area to find UA check-in and get BPs printed. That's when I found out I got SSSS'd. They went through my entire carry-on, shoes off, pat down, etc. at the gate.

On the plane to EWR I realized my onward BP didn't have PreCheck. Tried checking in multiple times and re-adding my KTN which didn't work. What did work for me was SDC'ing to the flight after mine and re-checking in which produced PreCheck. Ironically I gave up on the EWR Polaris Lounge and SDC'd myself back to the earlier, originally rebooked flight I was on. I had already gone through security so it didn't matter but I did get PreCheck on the earlier flight BP this time around.

-RM