T46G goes unreachable with EXP40 enabled.

[complex1]

Hi,

It could be that the monitoring process is asking to much power from your PBX in other words your PBX is not powerful enough to process 3x 87 BLF messages (Subscribe, Notify) at once or there is not enough bandwidth available on your network.
Please try lower the amount of extension monitoring, e.g. 3 phones and 2 ext. on every EXP40, and check if it will solve the issue.

If you are interested… Here is a short explanation how it works:
When an IP phone is configured to monitor an extension it sends a SUBSCRIBE SIP message to the PBX. If authentication is configured, authentication takes place and if the subscriber is successfully authenticated a 200 OK SIP message response is sent back to the subscriber.
A NOTIFY SIP message which includes XML in the message body is sent to the subscriber (in this case the phone) to advise the subscriber the current state of the extension being monitored.
Once status of monitored extension is changed from idle to busy or vice versa, the subscriber is notified from the PBX with a NOTIFY SIP message. The subscriber must acknowledge the NOTIFY SIP message by responding back with a 200 OK SIP message.

Hope this helps.