The Honeywell TCC API is not documented although for a short time someone had exposed some reverse engineered details. Those got taken down years ago... The result is as you'd expect, no document to turn to to say this is what's needed, this isn't AND far worse, Honeywell could have changed their API and would never have mentioned it publicly.
I say all this because the TCC API interface is horrid. Like everyone discovers, for no discernible reason the interface will reject connections. It's known that Honeywell limits use, and so there's a convenient excuse, but in my experience, the rate limit idea is inadequate. I think it does cover a vast majority (95%) of rejects. But I've seen others as I tried to streamline this driver over the years. I tried to determine if there was perhaps a change in the API that was at the root of the problem brought up a couple days ago... couldn't get a good answer because when I'm debugging, I hit the API at a pretty high rate... and get rejects.
I test 3 different ways: Homebridge-TCC, Honeywell phone app and this driver I maintain. I am forced to 'take a vote' when investigating because no one way works 100%. Yesterday, all 3 were failing (rejecting) at a rate I haven't seen in a long time. That allowed me to conclude, Honeywell was the root cause.
Someone in my house manually adjusted the temp today and I used the Driver to set it back. I hadn't touched anything Honeywell related in a day, so naturally my first time worked.
A decade or more ago a friend and I were discussing software debugging and the various methods individuals use. He and I were each managing different groups of developers in the same company and it was fun to compare and contrast... BUT he was concerned about approving expenditures for debugging tools. He would say: "It's a computer, it does what it's told to do. So?? What did you tell it to do?" Meaning the greatest debugging tool is your brain and if only you can think like a computer, the answer is clear. 
So I sat down and did some code review and can see a potential issue with "Resume Schedule." However, without documentation it's very difficult to say what it is supposed to be exchanging with TCC.
I will continue to review this at the rate Honeywell allows. 
Just a Note: "Follow Schedule" isn't an actual command to this Thermostat, as far as I can find. It's the absence of other Modes. It's when the Thermostat is NOT in Vacation Hold and NOT in Temporary Hold. What's left is: Follow Schedule. Seems to work in the sense that I removed a Temp hold and the Status in the driver changed to "FollowSchedule", matching what the TCC App was indicating. 
