Could you tell the firmware version you had before updating to RUTX_R_00.07.04.3? Also, did you perform the update with Keep settings option enabled? If yes, could you try resetting the device?
I have tried the update on RUTX50 as well, but could not replicate connectivity issues. Issues might be specific to your configuration or hardware.
I would like you to attach a troubleshoot file to your question. Make sure the device is upgraded and the issue is present, then access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there.
The logs in the file might provide more insight into the issue.