EDIT!!!: I swapped the Savox servo for the original one, and it's still doing it. It didn't happen before with the stock servo.
However I noticed something very weird. If the receiver's antenna isn't pointed straight onto the transmitter, some weird glitches begin to happen, for example losing some power for a few seconds, then losing the power completely and after a few seconds gaining max power, and the cycle continues. The weird glitches include the servo backing out at 100% turn signal.
I noticed that my 4S battery is very slightly bulged outwards on the top and bottom (I don't remember if it was like that or not). I checked the temps after run and it seems to only be a bit warm. Nothing special, just a bit warmer than my freezed hand (in Poland we have winter now) sooo... Should I be worried about my battery or should I replace the transmitter and receiver (as that may be the main problem)?