To check that the fault is not with your Remote, try changing to a different Ethernet cable. Preferably a short (6 foot) CAT.5e. I found that all the short Cat.5e patch cables I had at home worked (but not all the long cables). Maybe, length of cable is an issue for the remote (if the cable isn't exactly as specced by Kemper).
Like you, my long cable worked fine up until I upgraded to v7.0.9.
I note that with this version, the power up sequence for the remote is quite different, with nothing happening with the remote until my Power Rack is almost fully booted up, then the Remote boots up.
It would save a lot of trouble if Kemper sold or recommended a specific brand of Ethernet Cable.