Hello, I have the same issue. I bought two Nest Thermostats to replace 2 of my 4 24VAC Aube programmable thermostats. The previous owners have installed six 240V circuits with low voltage thermostats. The first install had a small issue because the relays use 2 wire cables, without c-wire. I had to purchase a nest power connector to remove the error E297. After all this, I tried to install the second thermostat, but it keeps failing on the wifi configuration. I reused the very same base of the already operational Nest thermostat, but to no avail. Still E297 error and no wifi connection. I guess it needs to be updated in order to detect the nest power connector, but no wifi means no update. E297 could also make the thermostat to shut down its wifi. I think I am trap in a loop for this one. I may have to return it or buy a plugable 120VAC / 24 VAC, temporary connect it to C and R. Maybe I should connect the W in C to provide power and maintain the wifi up during the configuration, as a test. Not sure.
