|That's an odd occurrence. |
Since you say, " Although sometimes it happens opposite e.g. lan is working but internet is not working." I'll assume you have shares created.
My suggestion at this point would be to first, make sure your router has the most up-to-date firmware. If it doesn't, and you upgrade it and that doesn't fix the issue, you may have to reset the router to factory defaults and then reconfigure it.
If the firmware is the most up-to-date, you may need to reset and reconfigure.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.