Timing chain issues

The newer design needs oil pressure to lock them but they shouldn't retract like that either. I would take a close look at the path the chain is taking and the sprockets as well. It's acting like the chain is binding down below the guide. The problem is that the oil pressure takes a second or two to reach the tensioner so if it jumps now it could easily jump when you try to start it. As a test try sticking something in between the guide and the tensioner position and see if it stays tight that way. You should be able to tell if something is binding that way.

Well that's a good thing. Take a look at this video and see if it looks like what you have done. I think I'm missing something but not sure what.
https://www.youtube.com/watch?v=1SC8Jy9NOJk

Okay, I asked a couple others and we all came up with the same thing. This engine gets put together, then the timing cover goes on and it is tight enough that the chain should stay in place on initial start. To check that one suggested setting it all up, mark the chains in a couple places, now put the covers on with only a couple bolts and rotate the engine some, see if the chain stays then. I know the GM info I've read doesn't mention trying to rotate the engine like you do many others.