I was just reading the prior posts. I was using the original code. I don't currently use MQTT for anything on HE. I was just going off to educate myself on an HE implementation of MQTT. Any help along those lines would be welcome but it sounds like you are quite busy right now fixing this.
LJ
If you have a driver for the thermostat I'd be happy to test. I'm currently using this one EcoNet/rheem-econet-thermostat.groovy at master · bmcgair/EcoNet · GitHub
Nothing special you need to do, you just need this code GitHub - dcmeglio/hubitat-rheem at mqtt_api
If you're worried about MQTT because you've read things where people talk about having to install other software, that's not how this works. This is just a client, nothing to install except the app and driver (delete the ones from the prior posts, they no longer work). Note that this new code is definitely still buggy. Rheem doesn't document how to use their stuff so it's a lot of trial and error.
I haven't yet looked at the thermostat stuff but I'd be happy to once I figure out the water heaters. I will likely need your help testing!
Yes, I was concerned that I would have to buy the Raspberry PI4 I have been considering for other applications to run Broker. I want to get a PI4 for some other apps, but I have been putting it off for various reasons. I thought this would push me over the edge. Oh well, I guess I will still wait 
OK So I loaded the new app and driver and get the same result. Rheem really messed up all these Home automation platforms without sharing their new API specs early before rollout.
LJ
It’s a private api. Most vendors unfortunately want you to use their apps and don’t support home automation platforms. Did anything show up in the logs?
The app threw these errors:
and the driver threw this one:
For the record, I added the device manually, by assigning your driver to a virtual device. I do not know if your app would automatically create one. does it?
LJ
Yeah the app creates it. You can’t create it manually. Do any errors show in the log when you got the no water heaters found message?
Let me delete the device I created and test again. It I. The last message I showed you the errors that the app had when I tried it and got the no water heater found message. I will test again.
LJ
OK, Deleted the device I created manually, and then tried to rerun the initial add of the app. I entered my User ID and password for EcoNet, and got the same error, No Water Heaters Were Found. The error below is the same one I had before.
I added some debug logging, could you grab the latest app and tell me what it logs when you login?
I'll try to set some time aside this weekend to do some testing and report back.
Been doing a lot of testing today and collaborating with the Home Assistant guys. We figured out how to fix the issue where sometimes the mode/temp change wasn't refreshing properly but as far as we can tell, ambient temperature and the current water temperature have been removed from the API. We're trying to setup a sniffer between the water heater and the Rheem server to see what it's sending, but so far no luck
Now, suddenly, the original integration is working 
Mine has been working. That is the strange part, not sure why it works for me and not others?
They might be phasing it out slowly. Mine was working for until Tuesday. When I connect to the old API I get stale data. It shows the ambient temperature from this weekend, it doesn't match what is shown on the display of my water heater. I also lost the ability to control it from the old API. Maybe it's a slow rollout?
I appear to get the data (that is available), but it also logs this error on every refresh:
API Get Error: groovyx.net.http.HttpResponseException: Not Found
Yes, as noted the integration is currently broken as Rheem completely changed everything. You are welcome to try the new version from GitHub - dcmeglio/hubitat-rheem at mqtt_api but please note that it no longer supports retrieving the current water temperature or ambient temperature as Rheem removed these capabilities.
Sorry for not being more specific .. the error was logged with the current (as of this morning) mqtt based code.
Download the Hubitat app
