Insufficient Ressource / M900 / 3CX

Hello,

We have a 3CX v20 with 3x M900 and 10x M70 in use at a customer. There is a call group in the 3CX with six extensions that ring simultaneously. The DECT bases are in multi-cell mode and LAN Sync is also active.

Delivery firmware: 4**.**
Firmware M900: 740.102
Firmware M70: 740.100

The error is that “Insufficient resource” appears in the display of the phone and you have to answer the call with several phones one after the other. I have seen the limitation that max 4 are possible with g722 and 8 with non HD. After deactivating HD via the 3CX template and reprovisioning the DECT bases, the problem is still there. 
I have also permanently assigned the phones to a base on the DECT bases to ensure that only 4 phones are connected per base. The problem still persists.

Occasionally there is also the error that “User active” appears on the display when you want to accept a call and then the phone rings again shortly afterwards.

Can someone help?