Ran into the same issue. Recommend installing the custom app [RELEASE] Device Activity Check - Get notifications for "inactive" devices to alert you when one stops pinging (dead battery or bad mesh).
I ran into the following issue when I tried to replace the batteries with Duracell:
We recommend using Energizer, Panasonic, or Maxell brand batteries which are confirmed to work well in the sensors. Our techs have been looking into a battery issue with the XS sensors and have confirmed that for an unknown reason at this point, Duracell batteries are not working well to power the XS sensors.
ZSE42 Water Leak XS Sensor FAQs - Zooz Support Center
I gave up on Zooz leak detectors and replaced them with with Aeotec Water Leak Sensor (Zigbee) and have been pretty happy with them (even with the high cost).