@Sunshine 

So I retried and reset the extender a couple of times and now I can acces the web interface again using the static ip. However it still does not allow me to ping the other computer nor does it give me access to the wider internet. Even though the default gateways of both computers are the same.
If I do not configure static iip such as on my phone the internet works without issue.

Without configuring static ip my phone gives the following (check attachment).

I am living in an appartment, do you think maybe the tp link is connecting to another persons network? It would suprise me as the networks should be closed loop. I must be doing something wrong.

  @vatsk  I am trying to do the same for another web interface and I am still facing this stuborn issue. Is there any progress on a fix?