Could you try to restore the device to the factory defaults? Please refer to this link for instructions: https://wiki.teltonika-networks.com/view/RUT240_Device_Recovery_Options.
What are the steps that need to be taken before the issue appears?
Also, could you attach the picture file below your question for better quality or send it to me in a personal message?
If the device reset does not help, I need you to provide as many details about the issue as you can. Also, I need you to send me a troubleshoot file. Please, replicate the issue, then access router's WebUI, go to System -> Administration > Troubleshoot section and download troubleshoot file from there.
I will forward this information to the development department for further investigation.