|Maybe there is a problem with the router.|
When the problem comes up, did you try to reboot the computer, that is connected wirelessly, to check, whether the connection is working after reboot.
In that case, the problem is located at your computer, connected wirelessly.
If it's still not working after reboot, the problem is most likely at the router.
Mostly, a firmware update helps on that.
Have you checked for the latest firmware for your wireless router?
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