Hello.
Thanks you for your feedback.
That is not a known issue, but what happens sometimes is that when you make a Ping too soon after the reboot, it fails, but not because there is a problem, but because the device is still waking up some interfaces and diagnostic tools and it can take around one or two minutes top fully wakeup all the internal scripts.
Please, test the RUT2XX_R_00.01.12 and please give us feedback. For that we will need not only the Screenshots of when it happens, but also the Troubleshoot files of the device after waiting a couple of minutes after you get the issue.
https://wiki.teltonika-networks.com/view/RUT240_Administration#Troubleshoot