i can ping the external and internal interface
i can ping the internal devices by ip and dns
i can ping domains on the web and do a name resolution. tracert gives also valid answers.
if i put a domain in the web browser, it says "website found" but has a timeout after certain time. (only for external domains)
if i update the network settings through web admin, imm. it starts working
It would be useful if you described your internal & external network topology and what each devices is and how it relates to the devices its attached to.
Can you boot an MD successfully on your LAN side NIC? If you attach another computer to your LAN side NIC does it get a valid DHCP address? Have you got a 2nd DHCP server on your LAN side?
All the best