Yep, this is how the MRCC behaves in my car as well, and from what I've read this is the correct behavior.
This sounds like there is a problem with your MRCC...at least according to the manual and videos depicting how the system is supposed to work. I'd report it to Mazda as they may have a software glitch that needs fixing.
As far as how/when the system is used. Well, I use it on the freeway or highway (basically any mostly straight, typically fast-moving stretch of road). As all of us Californians have come to realize, that highway can turn into a parking lot very quickly. And in that scenario, the MRCC can come in very handy.
I have had my 2017 CX-5 GT for about 2 weeks now and this error showed up a few days ago. Before this error started I could set cruise control as long as I'm going above 20mph, and as long as I would do that MRCC would go all the way down to 0 mph. When it came to a complete stop it would autohold by itself even if you don't have autohold switched on. When the car in front of you begins moving again you lightly tap the accelerator and the MRCC will resume.
This sounds like there is a problem with your MRCC...at least according to the manual and videos depicting how the system is supposed to work. I'd report it to Mazda as they may have a software glitch that needs fixing.
...Now I get the same error message as the OP and when I initiate MRCC (above 20mph) and my speed drops below 20mph the car beeps at me and flashes the error message on the HUD as well as info gauge.
As far as how/when the system is used. Well, I use it on the freeway or highway (basically any mostly straight, typically fast-moving stretch of road). As all of us Californians have come to realize, that highway can turn into a parking lot very quickly. And in that scenario, the MRCC can come in very handy.