The grounding issue has confused me a lot.
Does it mean I am better to connect all negative polarities/pins of all strips. There is thick blue wire I am not sure if it makes sense or not.
Coming back to my previous setup(with two PSUs), Galvanic isolation didn't help me understand the problem directly, however, it directed me to Ground Loop which in terms mentioned Galvanic isolation is a solution to Ground Loop.
So that would mean, in my previous schema, current from Group A strips will potentially flow back to the GND through Group B(going to back GND at B or going back to Group A Circuit, not sure)