RDS/VOIP-IPsec vpn | Latence,freeze.... Sophos XG125

hi everybody,

i need help for my problem with xg125 SFOS 18.0.1 MR-1-Builde 396

We have a fiber connection 10Mbits on site.

We have a VPN Ipsec site to site : site on XG 125 and datacenter on SG330 ==> VPN was stable.

We have on a site a little client DELL 3040 who connect to the datacenter RDS 2016 Server (terminal server) over this VPN. Connection via HTTPS 443 to the broker.

We have a phone to connect a PABX over this VPN . NO SIP. My presta disable SIP,Tiemout ... https://docs.sophos.com/nsg/sophos-firewall/18.0/releasenotes/en-us/nsg/sfos/concepts/VoIPResolveCallIssues.html

11-14ms latency over vpn when i ping my dc or other , 6-7ms to directly WAN

I wrote 1250kB on a traffic shapping global for my 10mbits link, i think is good ? Sophos count in kB and not kb.

PHONE:

All connection is ok but, on the site the client said to me : A phone degradation, sometimes when a call group come, one of this don't ring.

RDS.Terminal SERVER:

The client has a small freeze or latency when he's typping a word or other.

We have QOS on VOIP and RDS. 

Have you recommandation for this or experience with this? Bug from firmware and other.? 

thanks in advance, I'm a bit stuck