Just for confirmation and reference purposes if needed....
However, no harm in reviewing the manual first and doublechecking that all is as expected or should be. For example the LED's may change during the disconnects. May be hard to catch with only short (1-2 second) disconnects but if you place the router in order to watch you may see what happens.
Over all, intermittent disconnects can be a result of a loose or damaged connection.
If both wired and wireless connectivity is affected then the problem is likely on the incoming (ISP) connections serving the router.
Inspect all cables and connections. Especially any coax splitters. Small device with one incoming coax cable and perhaps 2, 3, or even 4 cables going out. Splitters can degrade fairly quickly as most are very cheaply made.
Look for signs of corrosion, damage, crushing, hard bends, etc. anywhere along the cable run. Any sign of damage.
Unscrew any coax connectors, blow out dust, dirt, moisture etc. May help stabilize performance.
Replace any splitters or cables that appear damaged, aged, or fail to firmly connect.