Has this ever happened to anyone, and what to do if it has

The heat to the water chamber cycles throughout the night depending on the setting and the ambient humidity.
Adaptive just means it uses the internal sensor in the machine to start with whatever the ambient humidity is...then it heats up as needed to try to maintain whatever humidity setting you have chosen gets delivered.
So expect it to cycle throughout the night and that's why checking it in the AM isn't so reliable. It might be working just fine and just happen to be doing the "off" part of the cycle when you get up. So it will be cold to touch but maybe an hour ago it was warm to the touch.

When working it never gets so hot you can't touch it. Or at least none of my machines that I have ever used in the past (even the ones that didn't have the adaptive sensors in them). Gently warm is about the warmest I could ever say they ever got. Certainly no where near warm enough to be classified as uncomfortably warm.

If it's using up water...it's working but the fact it doesn't seem to be using much water doesn't necessarily mean that it isn't working.
Let me give you an example of what I have learned over the years with the machine that do the adaptive thing...when the ambient humidity is high none of my machines ever used any water but when the ambient humidity is relatively low I might use up almost all the water in one night and never changed the humidity setting.
I don't know off hand which setting gives what humidity delivery but let's pick the setting of 5 as an example...suppose it means 85% humidity delivery. My humidity in my bedroom usually runs between 40 to 50% at this time of year...so if I use the setting of 5 that means the machine realizes it starts out at say 40% and it just needs to add enough heat to bring the humidity up to 85%. So it will cycle on an off in terms of adding warmth so that 85% humidity gets delivered. For me 40% is relatively low and I will use probably 3/4 of the water in the chamber.

Now some nights the humidity is a lot higher....it's raining or extra humidity outside which means that I have a higher humidity in the house...especially if I have the windows open and not running the furnace (either for heat or A/C which dries out the air)...and I have maybe 75% ambient humidity in the bedroom. Those nights the machine simply doesn't have to add much heat at all because it doesn't have to add much moisture to get up to 85% from the starting 75%.

I have a little gadget on my bedside table that tells me the ambient temperature and humidity in the bedroom. Some nights when I see 60 to 70% ambient humidity and I have about half a tank of water I know that I won't need all that water and not much chance of it going dry during the night. The most number of nights I have ever got out of a chamber is 2....my preferred humidity setting is a high setting and most nights I use in the neighborhood of 3/4 of the tank unless it happens to be raining or something like that where the humidity is just high everywhere including in my house.

Thank you, Pugsy, for the very helpful info on ambient humidity. Would you recommend the gadget you have, and if it is still made, could you provide the details of where to get it. Is it battery operated or a plug-in device?

The humidity gadget I got off Amazon and it was one of the cheapest...less than $10.

I don't know if Amazon still has it but any of them will do the job. Mine does temp and humidity and that's all I need.
You don't need expensive or fancy.

https://www.amazon.com/s?k=Hygrometer&ref=nb_sb_noss

I tend to go with cheap and best seller.
I think mine is the Habor one.

Here's a cheap one. It looks similar to several my son uses.

https://www.amazon.com/Amrka-Hygrometer ... 073PSPTZ6/