BP randomly squeaked?

[Bogertophis]

...He’s never had an RI but was diagnosed with stoma last year mid January, tested negative for an RI despite having bubbles in his mouth...

Please elaborate- not sure what you mean by "stoma"? Guessing you meant "stomatitis" which is WAY different than a stoma.

Humidity is not best raised or maintained by spraying, as you've already proven (yours has been way too high & then falls off- spraying/misting is a very temporary boost at best). Using the right substrate (one that holds humidity) & controlling air-flow usually works better. Also, 55-60% would be best unless your BP is in shed, & only then raise it to 65-75%. You don't want 80-90% at all.

Another thing you can do is provide a "humid hide" where he can get a lot more humidity without soaking his whole enclosure. A healthier option for most, IMO.

Squeaking sounds can also be caused by a little substrate or some remaining dry shed in a snake's nostrils (they're supposed to shed the outer lining of their nostrils- if some gets left behind, it can cause whistling or squeaking sounds when the snake breathes.