|Check for a newer version of firmware for your unit. If you find a newer one, download and apply it and see if the issue goes away. If it doesn't, your router may be in need of replacement. |
If you have a spare router, or have access to one you could borrow for a few days to test, I would do that. If the issue goes away, and stays away with a different router, it's fairly safe to say your router is going bad.
If however the issue persists with a different router, that's indicative of an ISP issue.