You’re welcome - I enjoy troubleshooting
Like you, I can’t see any reason why the fermentation would work for one recipe and not the other, and your methods and bowl situation seem ideal.
Are you using a different bag of groats or is it much cooler now? As I mentioned above, the fermentation to have it grow by 50% is around 24 hours when ambient temps are winter (mid 60s) and often less than 12 hours in summer temps around 80 F.
The recipe on Hormones Balance (HB) is basically the same, like you said, apart from the amount of groats. Was your HB loaf dense as well as flat? If it wasn’t dense, I suspect it was flatter simply because there are fewer groats.
Maybe do a hybrid and see if if simply upping the amount of groats – maybe to 2 cups – makes for the height loaf that you want.
Let me know how this goes and all the best to your son! Also, I love buckwheat and this recipe, but you might want to check out this recipe too if you’re looking for additional gluten-free breads.