I am having a similar issue but my plants are in week 6 of an 8 week schedule. At first I thought it was spider mites and I began researching the nearest places to get a CO2 setup. While digging into more research and letting a couple days go by, I came to the conclusion that the spots starting in the centers of the leaves was nutrient deficiency. Because you still have 2-3 weeks until flush, I would suggest increasing the P and K in the water your feeding them with or if your using dry amendments simply add a quarter to half feed top-dress.
My plants have had burnt tips since the beginning of flower. I read the burnt tips were nitrogen toxicity and not to worry about that in bloom as the plant needs those vegetative nutrients to continue producing large fan leaves that absorb the most light and hold the most reserve nutrients when flushing.
All research based advice as I am not an experienced grower.
