No no this is not bud rot my friend,
Are you still giving them calmag?
This can be due the over feeding with calmag.
So if you feed it give it a little less.
And maybe start giving it less nutrients. Because it looks like the leaves are burning up because they have to much nutes inside of them and to much heat and the LED is to close to the canopy!
Good luck my friend.
But 100% no bud rot don’t worry! She is just fine
I agree this is a nutrient issue, not bud rot. Could be going too high or low on something or more likely salt buildup in the media. Might not be worth chasing too hard at this stage. Check runoff and if it's stupid high give her a flush.
Try to pull out the damaged sugar leave. If there's bud rot it will come out easy and feel slimy at the end(you know when you feel it.
Or grab your bud right below the brown leave and bend it back till you can see the stem. If there is bud rot you'll see it.
Much luck and happy growing