“How does putting something over the string grooves cause problems?”
Not everyone is in agreement with that it does. My Hoyt Satori came with some kind of felt-like stuff over the string grooves. Rick Welch used to do the same things with his Dakota bows, but I don't think he still does.
The idea is that it is best if the string automatically seats itself in the string grooves after each shot, which should prevent it from gradually edging over to the side. Whenever you shoot the bow with string torque, you are bending the recurved ends slightly to one side or the other. The string will try to work its way out of the groove, but a positive groove will help it to center itself again. The original string groove will probably do a better job of this than a felt covered one. Of course, you shouldn't torque the string, but most of us are not perfect.
You should check your limbs for twist often, by putting one end of the bow on the floor and raising and lowering the other end in your hand as you sight down the string. You should be able to notice if there is any deviation in the straight line of the string as it enters the string groove. If you catch limb twist early, you can usually correct it by slightly counter-twisting the end that is twisted while the bow is strung.