definitley a strange one...how you have had no troubles in a tent where most people struggle with intense board setups and yet you run into problems in an open room where these lights do best?.
Normal light burn/bleaching or heat stress is different. This is something exclusive to these intense spectrum LEDs
are you saying normal light burn/bleaching is caused by heat? and you belive your burn is caused by photon intensity/ppfd?.
if it was ppfd you would see it in your par readings, if it was cross talk/overlapping high ppfd areas again it would be obvious in your par readings.
there is nothing hidden/mysterious or strange about hlg's spectrum, 800ppfd of hlg's spectrum will perform identically to 800ppfd of 95% of every other light out there.
im not saying spectrum cant/wont have an effect just that there is nothing in hlg's spectrum that would account for your problems not to mention the numerous grows you see on instagram ect where people are killing it with said lights at 1000+ppfd...
if its your lights causing this and from what you say it certainly seems like its connected, then something isnt right elsewhere...
the plants in the tent looked fine and certainly seemed to finish well, but some of the plants in your open room dont look great, it looks like the smallest plant at the front right of your room that looks the most unhappy also looks to be the one most effected by burn in the second picture...
even the very lowest growth looks off so it cant just be down to intensity/ppfd. what ppfd did you get to in veg when they burned the first time?.