I had this issue after flashing an ESP8266 connected to USB (not the server, but the laptop). I think what happens is that it tries to configure the device while it is still in flash mode right after flashing it, and for it to come out of flash mode, you need to disconnect the GIO from GND (which you would have connected to be able to flash), then restart the device (unplug power/replug) and then click the setup wifi again.
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