Analog telephony, two specific devices do not communicate with each other, what?

Question

Telephony

It is impossible to call a second number from one number, and vice versa. Beeps go, there is no reaction at the other end of the wire. All numbers in the office are tied to the first one for dialing, other devices work correctly with each other. Devices Panasonic KX7730, PBX TEM-824. The PBX configuration was not changed, the second phone was recently transferred from one port to another (there is only one access to these ports on the PBX). My hands are sharpened for something else, and having unsuccessfully dug up the documentation of all the equipment involved, I ask for help - at least where do I start?

Answer 1

the second phone was recently transferred from one port to another (there is only one access to these ports on the PBX)

decipher!