You can clearly see the separation, and I saw no contact between the upper and lower stages.
Sorry, but where can you see clearly the separation?
You can see clearly that after separation there was no recontact.
But you can't see the separation itself.
Both videos I know (this here and the life NASA TV during launch) do not show clear enough the junction of upper and lower stage.
But both show from different angles, that the top of the lower stage and the bottom of the upper stage start to move in the same direction right after separation.
It is highly unlikely, that this is a coincident.
In my opinion there are two possibilities and the second with the higher probability:
1. The separation mechanism (probably some pyrotechnical severed bolts) did not work as intended (one or some bolts broke too late).
2. The separation rockets of the lower stage were too weak for this test (the upper stage had no ullage rockets and no own thrust). The lower stage is in the slipstream of the upper stage after separation and was able to catch up after normal separation leading to an immediate recontact that pushed the lower end of the upper stage to the side.
I say "too weak for this test" and not too weak generally, because with a normal upper stage there might be no problem.
They should have used the escape system (without or with delayed separation of the crew cabin) to propel the upper stage forward in the very moment of 1st stage separation.
I wonder what would be planned in a real launch, should the 2nd stage start tumbling like here. I guess it would be immediate start of the escape system.
But I guess, the escape system was only a mock up.
Regarding the parachute issue, the comments on youtube so far are wrong.
It can be clearly seen, that all three parachutes open normally, but then one rapidly deflates and you can see it dragging half of the canopy above the plane of the two good ones and the lines. I guess, approximately half of the lines broke (or more likely their attachment point(s)).
What happened to the second was blocked by the cloud, but it drags part of the blue material so I guess a quarter of its lines broke as well.
I don't know how many attachment points each chute has.
Were it four, than two of the first chute and one of the second probably broke.
I am pretty sure, that will not happen on the next launch.
/Armin
PS: I speak of "separation rockets" but this is a plain guess.
Should they did not use any means of active deceleration of the lower stage during separation, the visited tumble of both stage would be no reason for questions, it would have been expected.