Optimum with AC1750 cable modem router all lights are solid green but no internet

Hi all,

This is the second time I'm having the same issue. I'm having my AC1750 router modem combo with Optimum service.

It worked properly for 5 months and 3 days ago, the internt went offline while all the lights on the router were solid green... I contacted Optimum and was asked to reboost the router by unplug the power cable and plug back in. The internet went back on but not as fast nor stable as before. But now it happened again, with all lights are solid green but no internet.

Everytime I contacted Optimum, they would said everything looked fine on their end and it's bc of the router I'm having is not their router... I wonder if this really is the case... Any insight is appreciated!!