Mold can lead to aspergillosis, and sometimes diseases can be made worse by secondary infections. Hopefully, soon, they will get back to you with information on the testing, and you can go from there. Sorry that you have lost another one. Here is a good link to read that includes many of the common diseases in chickens:
https://edis.ifas.ufl.edu/ps044
https://edis.ifas.ufl.edu/ps044
