Sorry I don’t understand the question… The only change I’m aware of is upgrading to a supported version of FreePBX. In regards to what activities cause the problem, I don’t know how we could determine that?
We’re a small business with about 20 people with phones(most rarely ever use the phone), and I’d guesstimate the maximum is about 5 simultaneous phone calls and that’s infrequent. I’m not sure what other factors would play into how much RAM Asterisk consumes… I just know from looking at htop /usr/sbin/asterisk is the process that is consuming all the RAM.