Note that the thread you posted this in is about the (newly released) FP5.* I am not aware of this being a common issue with the FP4, so you may just have a bad power button in your device (maybe a faulty connection or something). Since it’s only 3 months old you should easily be able to get a free replacement if that’s the case. Just make sure that you backup all of your data before that, as a factory reset will be necessary no matter wether you get a repair (that you do not perform yourself) or wether you receive a completely new one as replacement.
Edit: *Post has been moved to a new thread to seperate FP5 and FP4 issues. Thanks @Lidwien 