Any thoughts on what is happening with the leaf on...

Hello ! Well your plants can be bend with the LST technique but as she was slow during the first weeks you should not top or stress the plant too much (not recommended but you can , it's up to you) . By trimming I think you mean defoliation , so I'm not a defo pro , in your case it would be unuseful as your upper leaves does not block the light to your lower stems , even the effected leaf don't need to be cut before 50% is damaged ( I go to 70% as the plant still sucking the energy out from the old leaves). The only training I would do at that stage is to pinch the main stem just under the new nodes to encourage secondery stems growth. Concerning your damage leaf it can be heat like bulbi told you but the edges of the leaves would be burnt too ( not only the tips) , I would no bet on a deficiency as you'r using plenty of fertilizer ( do you check your ec/ppm level ? you should grab an ec/ppm pen to do so , it will help you to feed better) , but your plant looks pale like a Nitrogen deficiency , weird to me. I hope it will help you 😁👍