AIRPORT TIME CAPSULE INDICATOR BECOME YELLOW EVERY SO OFTEN. THE TIME CAPSULE IIS CONNECTED TO A ARRIS SURF BOARD MODEM WHICH IS CONNECTED TO OUR INTERNET CABLE.

You will get that yellow flashing light on the Time Capsule for these reasons:

1. Airport Base Station firmware update (2017-12-12) waiting for installation (if configured in Airport preferences).
2. A current network outage between your cable modem and the ISP. Usually, this will auto-correct, and you will return to normal operation. Sometimes though, you will have to reboot the cable modem yourself.
3. Any power outage. Same as [2].
4. Network compromise between cable modem and Time Capsule.
5. Other Time Capsule error

You are welcome. If that doesn't work, you can try the below.

See pages 28 and 29. Using Airport Utility (page 29), I don’t see the options the manual says are there. I have done a reset and a full reset (page 28) many times and it has always straightened out the Time Capsule.

Time Capsule Manual

Airport Base Station or Time Capsule Reset

check if that Arris is a cable modem and router. if yes then you'll need to place the Apple router into bridge mode and you do that through Airport Utility found in the Applications folder then Utility folder.

Have you tried resetting/restarting the modem?