One way call only, after restart intercom server issue resolved, very weird

Recently I installed FreePBX 16, and now there’s an issue with the intercom system. When the guardhouse calls the resident using an Akuvox VP-R49G device, everything works fine. But, when the resident tries to call the guardhouse using a Dahua VTH2421FW-P device, the call just ends like it can’t connect to the intercom server. Weirdly, the devices are connected to the server and the network is good, as the guardhouse can call the resident just fine.

After I restart the FreePBX 16 server, everything seems to work perfectly. The resident can call the guardhouse, and vice versa.

Honestly, I have no idea what’s causing this issue. No firewall in FreePBX and my gateway firewall is not blocking anything. Intercom server and endpoint are all within same VLAN.

What could be the possible issue ?