I bought two Tuya Zigbee moisture sensors to put in my fridges (since they keep flooding with condensate)
The sensors report manufacturer as by _TZ3000_k4ej3ww2 and model as TS0207 in Home Assistant
They pair with ZHA without problem, and show moisture/dry correctly
However, 6 hours after pairing they always become Unavailable and need a repairing to work again…
Anyone else using these, and how are you getting them to work properly?
How healthy is your zigbee network? The fact that the moisture sensors were working for a while suggests that you may not have enough routers to maintain a good connection - particularly as the sensors are inside a metal box. 
Also, are the sensor batteries sealed? I have a non-zigbee temperature sensor in my fridge and condensation build-up on the battery can be a problem, particularly when the battery has just been replaced. I keep it wrapped in a couple of ziploc bags with sachets of dessicant in them - though I suppose that’s not helpful for a moisture sensor. 
I may need more routers for sure, but these are the only things that fail. And it happens even outside the fridges - that screenshot was from them staying at my desk where I had them when I paired them.
I have the same issue with these water sensors on my network. No problems with other devices going unavailable.
I’ll add a “me too” here - this is the only sensor which won’t stay on the Zigbee network and whilst it’s marked as disconnected after 6 hours this is when timers fall over. It actually stops reporting moisture or pinging within 3 minutes of pairing being sucessful
This is on my desk and adjacent to the Zigbee coordinator, with 4 repeaters within 3 metres
Whatever’s wrong with these devices is consistent (multiple devices here and multiple reporters saying much the same thing)
WRT sealed batteries, mine are using CR123 cells (new from the packet and reporting 100%) which are HUGE and have lifespans which makes button cells seem pitiful - besides they’re sitting on my desk and condensation isn’t an issue
Is there something on the Tuya-branded zigbee bridges which keeps these things awake?
I’m going to add another “me too” to this. It’d be very nice if there’s a way to keep them online as (as you say) the large batteries and built-in beeper is a big plus.
Aaaaaand me, too.
Read and try to follow these best-practice tips:
I have the same problem. I tried with many repeaters, batteries, locations, … After few hours the device become unavailable and I have to click on its pair button to re-enable it.