Rear derailleur doesn't go to smallest cog I'm sure it is a simple fix to this, but please bear with me.
I have recently swapped my rear wheel on my bike (with an identical one, keeping the same cassette). Upon putting it back in, I noticed gears were not changing properly (chain was skipping or it wasn't moving smoothly to the next cog when changing gears).
I played a bit with the barrel adjuster, but before I managed to fix the problem I noticed that a. I could rotate the barrel adjuster infinitely in both directions and nothing was really &quot;moving&quot; and b. the chain wasn't going on the smallest cog anymore, no matter on which chain ring I was.
My questions would be:

Is it normal that gears need adjustments if I change a wheel with another identical one?
How can I fix the rear derailleur so that the chain gets on the smallest cog, and also fix the original problem of non-smooth gear changing?

Also, the barrel adjuster seems to be formed out of two components, each of them rotating independently (with the larger one moving vertically as well, with the help of a spring). Would appreciate some detailing of how this actually works. I have attached a few pictures.
I am talking about an Ultegra R8000 SS rear derailleur.
The inside of the barrel adjuster should screw into- and out of the derailleur  when you turn it. The part around it should only slide lengthwise but should turn with it (there is a slot which allows it to slide lengthwise but ensures they turn with each other).
In my experience the Ultegra R8000 barrel adjuster has an unusually fine thread and needs quite a few turns to move a real distance.
If your second rear wheel is really identical to the first one (same hub, same cassette, same spacers on the cassette (if any) etc.) then it shouldn’t require derailleur adjustments. But I guess different torque on the cassette lockring or some other minor difference could be a reason.