Roach droppings and smell behind drywall

We have a gross issue in our bathroom. I have noticed an odd, musty smell for a few years since we moved in. It only flares up when it’s really hot outside.

I opened the light switch and found a mound of droppings. ChatGPT says it’s roach droppings. We did have a lot of large cockroaches in the house when we moved in, but Orkin took care of that problem.

I cleaned the light switch and sanitized with chlorox wipes.

It helped the strong smell a good bit, but the smell is still there.

Any suggestions?

I’m thinking about using a borescope to look behind the light switch box, but from what I’ve read, droppings typically fall to the ground.

Oh, and we had the attic insulation sucked out, vacuumed, air sealed, and also added blown in fiberglass insulation. So there shouldn’t be anything leftover in the attic.

There’s no signs of any active infestation anywhere.