Boards tend to run hot but I suspect that the issue is a nutrient imbalance rather than heat from the board. It's very hard to cause damage like that with an LED. And a hang height of 18" is about right for a board light.
A symptom that weighs against this being light damage is that you've got discoloration at a variety of distances from the light. In the second picture, the cola in the front right is as damaged as the cola in the back but they appear to be at different heights. Some of the leaves at the soil level are damaged. Excess light would not cause.
Also, none of the colas appear to be impacted.
With an RH of 45% and temps as high as 31/86, your VPD is very high which means that your plants are transpiring a lot. If not properly watered, that can lead to serious nutrient issues.
The reading of 31° and 45% is at the base of the plant, at the soil level. If you check the temps at the flower tops, I suspect that your colas are at 90°+. Couple that with RH that's lower, because it's not near the moist soil and because RH falls as temperature increases, and your plants would seem to be at an extremely high VPD.
Have a look at the third photo, specifically the leaves just above the hygrometer. Those leaves are near the bottom of the plant but it's 30.7/85° and 50% RH. That's a VPD of 1.9 which is well out of range for a cannabis plant.
The sugar leaves on that big cola do look dark enough to have been damaged by heat from your light (which is not because they're getting too much light) but sugar leaves further down the cola have a similar burnt look. Excess light won't do that but excess heat will.
The environment is very hot and quite dry. The damage would seem to be a function of high heat and low humidity. I don't see anything that leads me to believe that too much light is causing the damage.
