I found the video from BigCliveDotCom that explains why these moisture sensors go bad so frequently.
The TL;DR version is that Amphenol the maker of the sensor states that these should only be driven by AC current, something that many designs simply do not do. If one drives it with DC–which requires fewer components–the sensor becomes polarized if DC current is applied. Which would explain why all those cheap Chinese hygrometers fail over time. He also explains what kind of mishandling can cause damage.
Near as I can tell, this is the only sensor being used on the market. It was invented by Telaire which Amphenol acquired in 2013.
Here’s a data sheet.
https://www.mouser.com/datasheet/2/18/AAS-920-060E-Telaire-EMD-4000B-110614-web-1315783.pdf
Here’s the segment that Clive references. I don’t think it can be any clearer than this.
I have a post that I put up here last year which showed me taking apart three of these hygrometers. All of them use the same sensor.