One router works another doesnt (yet another "cant connect" issue)

Hi,

I had some issues with my current installation on a RPi3 that I traced to a faulty SD card. After getting a new one it worked again, I restored succesfully from back up and all was good.
I had some other issues with all the addons not wanting to start but even that got fixed with a clean install and partial restoration.

In the process I did multiple clean installs on my office network and that worked great as well. It took maybe a minute from powering up the RP to being able to acces the webinterface.

However when I take my restored RPi back home, where my current HA setup has run for 2 years, I get only timeout errors from my browser.
HA shows up on the router almost instantly when I plug it in, but no matter what adress I try to call I cant connect.
Also weirdly enough im not able to ping the HA ip adress.
I have done nothing to the router config and no firmware upgrade to the router has happened.

I tried a clean install in my home network which got me to the installation screen, but when I try to restore from backup or restart HA I cant connect afterwards.

Does anyone recognize these symtoms?

Cheers
F