From what version of FreePBX to what version? Asterisk was not touched? (I should also add that 16 is end of life and no longer receives security fixes)
I’ll also go into memory usage a bit. Asterisk is a huge application with lots of functionality. What parts of Asterisk are used determines the code paths, and the memory. There shouldn’t be a leak of course but determining the code path and how to reproduce it can be helpful in identifying it.