There are certain pests that only come out when its dark and you dont see them. Then they go back into their hiding places, wherever that can be.
I believe they usually feed on the most tender young leaves.
The plant has been inspected during different times at different hours. Really, there are no bugs...
Up here in Canada I’ve seen this happen to a leaf that was touching cold window glass. It was warm inside, but outside about 5-10C. Same type of damage as yours showed up a few days later. I did spot treat with peroxide. It dried the spots, but leaf declined anyway and lost the leaf. Nothing else happened, plant carried on as normal.