Sharing my experience in case it’s useful for anybody else.
I have 33 devices registered through Tuya Smart and in HA with the Tuya integration. Several of the power plugs were going unavailable very often, but one in particular was annoying. It was connected to the washing machine in my outside laundry, and was regularly screwing up my automation to detect when the washing was finished.
I have a very old very solid brick house, and the wifi was patchy outside, so I tried installing a powerline extender, but it did not improve matters. I have two fuse boxes and had to put the extender on a plug pack against recommendation, so perhaps not surprising. I also tried two of the local tuya HACS addons, but they seemed to make matters worse - perhaps because now two integrations were trying to access the inaccessible.
So I got jack of it, and swapped the Tuya plug outside with a Zigbee plug from inside. Surprise, surprise, none of the plugs have been unavailable for the last couple of days, including the one from outside that is now inside on a different wifi network. I still have two plugs on tuya-local and they’re stable too. Right now there’s no imperative to move more onto tuya local because cloud seems fast and I haven’t had internet problems for over a year.
So my message is, if you’re having trouble with Tuya, maybe try unplugging some for a while to see if anything changes. Perhaps spotty wifi on one can cause problems with others.