Hello,
To have a better estimate about your case, additional details are required such as, device model and firmware version.
It would be most helpful, if you would attach a troubleshoot file to your question. Please, make sure to replicate the issue, 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.
Best regards,