I recently had this happen to me when I replaced my T5 nursery light with and HLG V2 4K. They plant kept growing, but the stems turned purple and the leaves were lemon yellow. Decent grow conditions in the basement 68F - 50%RH. I'm stilling learning the VPD crap and all so I figured it must be that the HLG V2 ran so cool compared to my other LED light, which is three HLG QB288 run at 450W. That light never gave me deficiency issues.
So, if the plant is slowly transpiring why would you only up certain nutrients and not bump total EC?
I'm also thinking of trying some off these next to the HLG V2.
Amazon.com: Simple Deluxe 25W 2-Pack Mini Ceramic Heat Emitter Reptile Heat Lamp Bulb No Light Emitting Brooder Coop Heater for Amphibian Pet & Incubating Chicken : Everything Else
The two plants got moved under my 4ft Veg T5s and they bounced back in a few days.
Now I have time to figure out how to mount those ceramic IR heaters to the HLG in a way that doesn't look like a ghetto hackjob.