Hi, and welcome to the forums. Thanks for posting.
Yes - we’ve heard of this issue with compounded sirolimus from many sources over the past few years:
Here: New Peter Attia interview w/Matt Kaeberlein, inferior bioavailability of encapsulated rapa
Here: Bioavailability of Rapamycin From Compounding Pharmacy
And there is an additional problem with Dan’s suggestion with the China-supplier of powder option; the Chinese suppliers are famously unreliable for quality of product, so you are likely to get something contaminated and/or not of high purity or quality. The HPLC testing by a good analytical lab costs far more (frequently between $500 to $1,000 and even then its hard to know what impurities to look for if you don’t know the details of the manufacturing process and inputs).
So yes, for 99.9% of the people who visit here, regular tablets from proven sources is the best option.