OPNSense small dropouts

[chris83]

we run an OPNSense VM on Hyper-V as a firewall behind a FrizBox.

-> FritzBox -> OPNSense -> GreenNetwork (incl. voip-telephone-system)

Every now and then we have small dropouts during telephone calls or while using rdp session from extern via vpn (openssl) to a computer in the green network. These dropouts are about 1 second and coming up every 2 or 3 seconds.

We implemented outgoing and incoming NAT-rules and traffic shaping like bloged under: https://docs.opnsense.org/manual/how-tos/shaper.html

The voip server is hosted extern on easybell. The easybell support told us, that sometimes there zero TCP-packages.

Does somebody have an idea how to solve or deeper analyse this problem?