The areas of the PCB that look like a green checkerboard pattern are tied to ground. Looking at your pictures, I see several areas where solder dross appears like it could be bridging the solder pad to ground. I also see several places where the soldering appears to be insufficiently filling the pad.
I am reluctant to blame your solder, because a two dimensional picture often has shadows and other artifacts that make things appear to be an issue when they really are not. However, as Grandma always told me, “Cleanliness counts”. I would suggest touching up all the insufficient solder areas. Then get some rubbing alcohol and an old toothbrush and remove all the solder flux, solder dross, solder balls and other stuff from the bottom of the PCB. Give it a couple of good rinses with a squirt bottle. Q-Tips are also good to mop up between component pins. You can either air dry it or use compressed air to dry the board.
After the board is good and clean. The visually inspect your soldering with a magnifying glass. Look for cold solder joints, insufficient solder, and solder bridging pads. Once everything passes inspection. Power it up and see if your symptoms are still there.
Skeptics may wonder why this could possibly be a problem. The issue is that solder flux residue attracts moisture and can often be conductive. It is like sprinkling a ton of high value resistors all over the board.