Good thought re ONT, though it hasn't seemed to be an issue - is it good practice to cycle it periodically? Sonic sent new SmartRG SR515AC router (same as what I have now, which was also replaced after the first time the internet service started dropping, about 4 months ago) - BUT, it was DOA, so now waiting on next replacement. Thanks for comments!
You shouldn't have to reboot the ONT periodically but it also shouldn't hurt. If you are noticing service interruptions or slow downs, a good rule of thumb is to reboot the router first, test, and if issues persist, reboot the ONT. As for the replacement router, it may be a good idea to upgrade to the Eero mesh network which you can do so through members.sonic.net.