Fresh OPNSense install slow web ui/1000 to 10000ms Ping times to 192.168.1.1

[HelloOPNSense]

Hey guys,
I just installed opnsense (newest version) on one of those 4x2,5gbe devices from amazon. When I try to connect to web ui it takes very long and often times doesn't load at all.
When I try to ping 192.168.1.1 I have ~40% packet loss and an average ping time of ~6000ms.
The routers wan port ist not yet connected to the fiber modem as it gets delivered some time later this day. The LAN port ist connected to a cheap 5 port gigabyte switch. In this switch is my main computer and a Fritzbox in ap only mode and another fritz repeater.
Thanks for any Help, have a good day!