DIAGNOSIS Weak signal or a glitch in the microwave's Wi-Fi module. The 2.4GHz band it uses doesn't penetrate the metal cavity well.
FIX Move your router closer. In the SmartHQ app, delete the microwave from your account. On the microwave, hold the 'Clock' button for 5 seconds to factory reset the Wi-Fi module. Re-add it as a new device.
IF THAT DIDN'T WORK The Wi-Fi module on the main control board may have failed. It's integrated, so the entire WR55X10942 control board must be replaced.
HEADS UP This model only works on 2.4GHz networks. If your router broadcasts a combined 2.4/5GHz signal with the same name (SSID), it can cause connection failures. Create a separate 2.4GHz network for it.