Timeout on non-critical invite transaction

In my system a chan_sip warning comes up regularly:

WARNING[2447]: chan_sip.c:4120 retrans_pkt: Timeout on fff451ba69f31c38983f7bf25b200555 on non-critical invite transaction.

I see this being a common question but I am asking again as I could not find a guidance to fix my case and any advise is highly appreciated.

First: is this a problem to be concerned about ?
Apparently the system is working … I can make and receive calls

My phones and freepbx server are all on 192.168.0.x behind a router with fixed public address

On the router:

  • SIP ALG is disabled
  • Ports UDP 5060 and 10000-20000 forwarded to Freepbx box IP

On the Chan-SIP settings

  • Public IP inserted correctly
  • LAN inserted as
  • NAT = Yes
  • Canreinvite=NONAT

I have tried to put every possible combinations of NAT and Reinvite settings, including disabling the Freepbx firewall but apparently nothing has changed.

I am running latest FreePBX and Asterisk 13

Where else could I look to troubleshoot this ?
Many thanks