Ye looks like a bird poo.
At night the plant performs cellular respiration.
H2o molecules are released from the stomata on underside of a lead, this forms little pockets of moisture underneath each leaf that will not move until air takes it away.
If the moisture bubble is not removed the processes within that specific leaf will cease, in the morning you may see small white residue on leafs that looks similar to what you have.
Although it does look more like bird poop.
Simple remedy is provide a nice flow of air constantly at night.
Seems ro be other problems afoot.