I solved this issue by installing 3rd party DD-WRT firmware to the C7 (2018 january beta firmware). There I was able to set DHCP mode to forwarder and now the switching between wifis borks both ways.

Model : Hardware Version : Firmware Version : ISP : Model : AC1750 Archer C7 (bought in EU, Hungary) Hardware Version : Archer C7 v2 00000000 Firmware Version : 3.15.1 Build 160616 Rel.44182n ISP :...

Did it start behaving poorly after working correctly for a while, or has it always been like this? Is the connection bad everywhere, or does it get better if the device is closer to the router?...