I suspect that the key clue here is the vibration in the upper chord when on the smallest sprocket
(exclusively?).

I read that as indicating an engagement/disengagement issue, possibly caused by the rollers touching the corners of the next tooth as they swing clear. This really isn't all that rare on brand new drivetrains, because the smaller sprocket makes this a critical tolerance zone.

The good news is that the least amount of wear (hours, not days) will break down the corners, and also increase free play at the rollers, either of which solves the problem.

Other factors may include chain line and/or burrs on the sprocket teeth.

In any case don't obsess over this yet. Ride the bike long enough to break in the drivetrains and see if it resolves, before wasting time over what may be nothing.