The one plant seems to be struggling and I’m not...

hey there Dan, you're basically right on all points but the root cause is actually overwatering, what happened was this plant has been chronically overwatered leading to too much availability of the N in the soil, and the heat provided the perfect conditions to incubate "water mold" which has affected the roots leading to that "taco-ing" you're also seeing in the other plants. Pretty important to sort that root mold on the roots otherwise what happens is that plant can wilt and eventually die like the worst one you've got there. You need to follow a very strict wet/dry cycle and accelerate recovery by breaking down problem roots with a chelation agent. Examples of chelation agents are enzymes, amino acids, humic and fluvic acids, beneficial bacteria (but these are slower acting!) and synthetic flushing agents (faster acting!) that you can dilute a bit more than recommended. This problem is very much common so dont beat yourself up ! Hope this helps ! 🚀