If possible, kindly check the logs of your RUTX50. This can be done by Logging in to the WebUI, then navigate to System → Maintenance → CLI. Then log in as root then use the same password in your WebUI.
Once logged in, execute the logread or logread | grep wlan0-1 commands and check the information regarding WLAN similar below:
Make sure you properly put the right password for the external AP.
Make sure there’s no conflict with the IP addressing (meaning the LAN IP subnet must be different from the Network subnet of the external wireless network).
If the things above have been confirmed and the issue persists, what you can do is to upgrade its Firmware Version to the latest one without keeping settings.
To do this, download the latest FW version on our Wiki page → RUTX50 Firmware Downloads - Teltonika Networks Wiki
On the WebUI, navigate to System → Firmware → Update firmware. Disable the keep settings option, then upload the downloaded firmware and proceed. Note: Re-flashing the firmware without keeping the settings will erase all the configuration of your device and there is a chance that you might lose remote connectivity access if it is configured.