in my case, after an extensive research I found out the problem wasn’t really ACS but the external restapi, which still takes too much time to answer the Extension script. It does work fine if it’s just a few connections. That, and the limit of 150 simultaneous connections on MariaDB.
As a general solution, current talks are about tagging CPE on boot event and process each one of them later using an external script. Also, we were talking about replacing the data retrieval from restapi with text files located on the same ACS computer for each CPE, that would speed things up, provided NodeJS does not cache them (I still have to research about that).
At the time, to solve the periodic inform interval issue, what I did was to write a single function which returns a number in seconds between 10 and 14 hours based on the last 4 digits of the serial number. Since then we had no more problems of collisions.