We don't see any distinctive insect damage, as the lacy parts of the leaf probably just disintegrated and broke apart after the tissue in that area died. If insects were at least partially responsible, a generalist feeder like grasshoppers, katydids, crickets, or perhaps certain beetles might have come and gone already, where no treatment would be needed since they are not longer present. Thrips can cause scarring and scab-like damage to foliage, but we don't see evidence of their typical damage in the photos. Instead, the tissue damage could be from over- or under-watering, or infection by some type of leaf spot organism (probably fungal). The black spots that look like spore structures within the brown areas might indicate a fungal disease, though it could also appear from fungal decay of the already-dead patch of tissue and not from a pathogen actually causing damage. No fungicide or insecticide is recommended at this point, though you can see if the browning spreads after the plants were moved inside, which would suggest that insects weren't involved.

Queen of the Night (Epiphyllum), as a jungle cactus, doesn't fare well if it gets as dry between waterings as other cacti prefer. Since the leaf damage is likely environmental in nature, has the container been monitored for watering needs often during the dry weather we've been heaving (recent rains aside)? Or could the container be getting too much water, such as if a saucer collecting drained water is not emptied and seeps back into the pot's drain holes?

Miri