Strange problem with two trunks on outbound calls

Hi, i have a strange problem with freepbx 2.11 and asterisk 11.16.0
I have set two trunks and many extensions.
Some extensione are in range 100-199 and others in range 300-313.
Every extensions has own Outbound Cid set on extensions options.
The strange thing is, sometimes in random mode, when an extensions try to calls out, using the trunk, i received "Received response: “Forbidden” from sip:[email protected]_freepbx;tag=as0f68b597’
Everyone is busy/congested at this time (1:0/0/1)
NoOp(“SIP/316-0000010b”, “Dial failed for some reason with DIALSTATUS = CHANUNAVAIL and HANGUPCAUSE = 21”) in new stack.
If i remove the outbound CID, there is no problem.
I don’t know what is wrong, can you help me please?
Thanks in advance