PM is almost definitely from humidity - but you should be able to control it with good circulation. could also be from condensation, or spraying your plants just before dark - better to spray just before lights come on like 10mins. I'm coastal, my humidity generally sits at 70%+
When you make your hydrogen peroxide (H2O2) mixture, start with a 35% or 50% concentration - get it from https://gthydro.co.za/products/273-h202-1-liter.html?search_query=hydrogen&results=1 (it must be food grade) using 50% - 60ml h2o2 to 940ml of water will give you 3% solution. anything weaker will just help the PM, anything stronger will burn your plants, again spray in the morning just before lights. your plants could have easily been helped, h2o2 & a bud wash after harvesting.
Make sure you clean your grow area thoroughly otherwise it will creep up again, air filters too