Not sure how you have everything hooked up but with the Powerwall2 configured correctly, unless you lose power for hours/days or have serious load during a power failure you should be able to keep the Sense monitor and your wifi network powered throughout. The nominal load of your network gear and Sense along with a fridge/freezer and other crucial gear should run for a long time on a Powerwall2.
As far as the Sense monitor reconnect:
Perhaps the Eero mesh is the culprit or are you hard-wired between hubs?