Do you know the capacity of the power supply? Output volts times amps = watts. 5V and 2A will be 10W for example.
It’s possible that your sensor dropping off is also power related, perhaps you have too much “stuff” (I know all the technical terms!) hanging off of one too small, power source.
If you have a multi-meter, stick it into circuit between battery + and board, and measure current. I suspect you will be drawing too much, causing the brown outs. Either this, or you have a dodgy sensor somewhere that may be shorting some power to ground.
All guesswork of course, but potentially helpful.