Strange behavior of asterisk, falls off, the trunk is exactly at 9 pm, how to find the reason?

Question

Asterisk

Good evening colleagues, after moving to a new office and changing provider to mts, the PBX began to behave strangely, every evening a week later, the trunk drops at exactly 9 pm, like an alarm clock, until the morning. Registration is in the morning. Registration goes through whats Rostelecom. Where can you start digging? There were no problems in the last office, no one climbed into the conference. If the registration host does not respond to ping, Yandex pings.

Answer 1

Obviously, you need to start with the technical support of the telephony provider