All, have had these sensors for a few years and struggled with the same issues and tried a variety of the remediations to little help. I made another run at things a few weeks back and discovered that there was a new firmware for these devices and by default the firmware upgrade for zigbee devices was disabled by default in my account. I reconfigured to allow upgrades and after about 24hrs all my devices completed the update (it only allows five at a time so it can take awhile). It has been two weeks since that and I have had zero issues with the devices going offline.
If you haven’t already done this then I highly recommend upgrading the firmware on these devices as for me, I finally seem to have a stable environment after two plus years.