Problem with propionate ester is his fast re-crystallization . Pharma companies they very well know why they have 50mg/ml only.
So could be ( I know its from one side funny reason ) that very thin carriers - like is Miglyol, or good MCT - carrier oil with BB are absorbed faster than active ingredient ( because of 100mg/ml concentration ) and this leads to re-crystalization in muscle.
But short ester is not always reason to higher risk of crystallization. Testosterone Acetate need smallest % of BB and is not so prone to crush.
And little surprise

I know that many of ,,UG,, labs they are using TPP instead TP. Because phenyl-propionate ester - testosteron , is more painless than propionate and need around 5% less of BB.
There is more theories and myths around brewing. Some people trust that EO is the worst solvent. And you can see - the best propionate ever pharma grade Farmak 5% from Ucraine is in EO and never ever heard about any issues with it.
Purity and quality of BB,EO is very important and find this substances at 99% pharm grade quality is not easy ( and I do not belive that some ,,lab suppliers,, that they have pharma grade )