I cut a few stems under my autos before they started stretching. LST has been a part of the game too.
As soon as Inmade that move a few days ago, plants begin to have yellow leaves
Any idea of the problem?
I think it is coincidental. Lower leaves will usually begin to yellow at some point. I usually defoliate those when they are > 50% yellow. It is actually a good practice to defoliate lower leaves that don't receive great light as it promotes top growth and better airflow under the canopy. It could also be a result of a lack of nutrients but your tops look lovely so I think it's just time.
Any yellowing indicates a problem unless its so thick canopy it don't get light to leaf .at the very end of flowering they yellow cause they pack phosphorus in the flowers. You could have slight salt build up .but plants should be green why people think its normal to have yellow leafs bs
The yellow leaves I'm seeing in your photos are of no concern whatsoever... trim them off as they're not doing the plant any good and rest assured, it's quite normal.
Good luck!