I think that your cooking time was far too long, and it sounds to me as if the curd became overly dry.
I make Berner Alpkäse, an alpine cheese of course. The rule here is to add culture and rennet together at 90 degrees, let sit for 30 to 35 minutes at this temperature (when making big batches like we do it will not loose any temperature while sitting) Then using a cheese harp, cut to curs the size of coffee beans or a grain of corn. It is very important that the curd be turned over while cutting so that the curd on the bottom gets cut also.
We heat it over a period of 25 to 40 minutes to 120-125 degrees depending on local conditions and the maturity of the milk. It is important that it be stirred quickly to keep curds from clumping. Then once at this temperature it is stirred for 5 to 15 minutes until the curds seem right. If they get rubbery then you have cooked too long.
Then we let it set for 5 minutes so that the curd can settle to the bottom and mass together, and at this point it is removed as quickly as possible, after the proper amount of whey has been removed for culture.
The curd should be let to set for maybe 30 minutes to 1 hour so that excess why can drain off, and is then formed and put under the press, and we press it heavy.
I press for 20 to 24 hours before brining, turning at least 6 times, and my cheese is not fragile at all, after the first or second turning it should be well massed together and if it cracks at this point then it likely will not ever stick back together.