It's difficult to diagnose if what you describe is a consistent trait or a problem.
What is consistent with a battery with low juice is your brief description of the circumstances leading to the display of symptoms. For Sabers with Sound, Battery powers SoundBoard and LED. When said juice is low, there's a
Force-struggle between them and motion/clash sensitivity is usually the first sign with little to no movement then there's also slight deterioration with blade illumination/brightness. If a solid charge hasn't been done for a couple of days since you got it, it
may explain above.
Personally, after unboxing, I do a general observation of the exterior and removable parts then power-on to ensure electronics work before plugging-in until light goes Green to then follow-up with a more detailed assessment.
Do the described symptoms still persist?
If in doubt, SFCS is your friend and like seeing your GP when you're feeling off, an email to them will get you sorted.