This is to with neoStat WIFI which has a single WIFI sticker near the screw at the bottom. These do not connect to a neoHub, instead they will connect to your router's WIFI directly.
If you find one of more neoStat WIFI going offline and keep going offline, it may actually be used to WIFI extenders. We have come across cases where they actually slow the Internet traffic down.
For testing purposes, power down the repeaters one by one and see if the thermostats return to being online after a couple of minutes.