A hormonal surge/puberty will not suddenly cause a rabbit to not eat hay. There are some things you can do to promote hay appetite: https://wabbitwiki.com/wiki/Hay#Encouraging_your_rabbit_to_eat_hay
In addition, there can be a self-promoting cycle rabbits get into where their selective hay eating leads to dental discomfort which then leads to reluctance to eat hay because it is not pleasant…. so if there may be a dental-related reason for the reluctance currently, it would be wise to have your rabbit assessed by a rabbit-experienced exotic vet to try and get a dental exam and see if molar spurs or something may need to be addressed to promote hay eating once again. Note an owner cannot see all of a rabbit’s teeth on their own — a vet needs to do it with the proper tools and sedation, if a more in-depth look is necessary. Signs of dental discomfort can include drooling, fur loss around the mouth, eating food then spitting it out, and selective food eating (e.g., will only eat veggies, but not hay).
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.