MultiWAN Problem - Connection Break randomly of some clients for outging traffic

[ArbosIT]

After correctly* configuring MultiWAN and change the Gateway on the LAN-Rule from Default to this MultiWAN Gateway, some of the Clients (and Servers) can randomly not communicate with the Internet at all.
(* i hope correctly - I used the manual: https://docs.opnsense.org/manual/how-tos/multiwan.html)

This is the only opnsense Firewall I have with MultiWAN / two Internet Lines connected, so I can not check this on any other Opnsense.

I get this failure messages in the Gateway Log File:
2022-10-05T07:40:36   Warning   dpinger   send_interval 1000ms loss_interval 2000ms time_period 60000ms report_interval 0ms data_len 0 alert_interval 1000ms latency_alarm 500ms loss_alarm 20% dest_addr 213.160.40.2 bind_addr 213.160.63.81 identifier "WAN_1_GGMAUR_DHCP "   
2022-10-05T07:40:36   Warning   dpinger   send_interval 1000ms loss_interval 2000ms time_period 60000ms report_interval 0ms data_len 0 alert_interval 1000ms latency_alarm 500ms loss_alarm 20% dest_addr 195.186.4.162 bind_addr 109.164.201.57 identifier "WAN_2_SWISSCOM_GW "
(GGAMAUR and Swisscom are both Internet Providers - so both WAN Interfaces named on them)

In the Firewall Rule Logs there are non packets logged from this clients that can not connect to the Internet.

If a client randomly has this problem, it could be that he can communicate again 5 minutes later and again a few minutes later he can not communicate again.

I am hoping for any help of you, I am mostly using other Firewalls than Opnsense yet, so I am not specialist on this system - but I have long knowledge of Firewalls and built MultiWAN already with Zyxel, Watchguard, SonicWall, etc.