In your z2m interface, are the devices in question actually online? Are they reporting any info?
You might try re-pairing them.
Have you added devices recently? > if so, does your dongle support having all those devices or are you at the max capacity?
Are the devices that have stopped reporting anything close to Wi‑Fi devices?
I’m experiencing the same problem, and the various attempts — changing the battery and re-pairing — do not restore normal operation. This isn’t the first time the sensors have stopped reporting data, but this time three of them malfunctioned within a short period.