Question about low yield batch

My last grow yielded a pathetic amount and I don't really see why. It gave 20g pr plant. Didn't even know that was possible. Bruce Banner strain. Normal feminized.

Everything looked normal, no problems during the grow. It even felt like a big yield when I harvested. But after drying when I weighed it I realized it was a new record low.

I have two theories:
I used some new lights, they were supposed to be better than my previous ones but maybe that was just a lie.

I also switched them to bloom very early. Using a SOG setup so I switched from vegetative to bloom 3 weeks after I planted the seeds.

Could this be the explanation?
Any other reasons?

Could be that you flipped to early or harvested early , let’s see some pics

photos of the grow and of plants when they where cut?

it could be anything.low feed or lights too far away. over watered or underwatered it would cause your plants to slow weeks in 1 fuckup....
harvested a few weeks early you could lose more than 20%

you have to give more data about your grow operation