Rod
Can I suggest you do the same experiment with some headphones plugged into the montage. Then you will know if the issue lies with Montage or your sound system

Sorry, you are experiencing this issue with your gear. As you see I do not think it is something you should ignore.

You'll need to describe in better detail, your system setup. No mention of Local Control means we have no clue as to whether the issue is a simple routing error or gear failure related. The mixer was unlikely the cause of your issue because it works generally on the 'speed of light' theory of electricity and signal passing through it.

One of the things that can make a difference or cause such issues, is signal routing related, in particular routing that includes multiple clocked devices (check), no clear master/slave defined (check), a potential MIDI loop situation (check). You seemly have a potential situation where trouble could occur. These situations are to be avoided unless you take care specifically to prevent issues. For example, how your gear resets needs to be known so that it doesn't cause the problem every time you power up.

You may have been ignoring it, and then working around it, but to me it could indicate a serious problem that you should spend some time tracking down.

First thing I would do is (really) simplify your setup. Just to illuminate all possible looped conditions.
Here's how:
Disconnect all MIDI cables and USB cables from the MONTAGE
Set the AUTO POWER OFF = OFF
[UTILITY] > "Settings" > "Quick Setup"
Touch "Standalone" - this will make the critical MIDI and Audio I/O settings to restore the MONTAGE to its most normal state

Make sure it plays normally: Connect headphones to the MONTAGE Phones jack (eliminate your auto power off speakers completely***). We are only concerning ourselves with MONTAGE in this experiment.
Power down your MONTAGE ... wait 10 seconds
Power On the MONTAGE
It should be completely booted and ready to play within approximately 17 seconds of flipping the switch On

Let us know.

Hello Sean and BM - thank you. I was concerned that it might be more serious than I thought. I switched on as normal to begin with, everything still connected as usual, and as usual I had to strike a key 4 times to get the sound. I would add here that once the sound is there, everything plays normally - no delay, and it stays that way so long as I don't leave it for any length of time (shortest so far has been 20 minutes).

I then disconnected the MIDI Out connection to the Tyros In, then the Tyros Main outputs to the Montage A/D inputs. Then the Main L/R Montage outputs to the Rokit speakers. I checked that the Auto-Off was switched Off. I went into 'UTILITY' - Settings - Quick Set up, and touched 'Standalone' (it was already selected). It flashed green when I touched it, then went off. My headphones are always plugged in, and the Montage played normally on several Categories and Pfs.

I powered down the Montage, and waited 10 seconds (clock timed) then switched on again - 19 seconds later (clock timed) it was ready to go, and played normally without delay (as it would have done anyway in such a short time). I have now been away for 25 minutes, so will go back and try it now. Usually I would have to strike a key several times to hear the sound.

OK, I'm back. I put the headphones on and struck a key 29 minutes after leaving - it played instantly. No delay whatsoever. I should say that I have not disconnected the USB cables to the computer (I forgot that) or the external monitor as the Montage monitor won't work (probably needs re-calibrating) - but as there's no delay it would seem to be nothing to do with the USB connections, but I will leave it for another hour, then try again, to be sure.

Right, done that, 1 hour and 2 minutes after leaving, I went back to the Montage, donned the headphones, and struck a key. Instant response, no delay at all. Plays normally too. So I guess we can rule out the USB connections?

I'm sorry, domestic arrangements mean I'll have to shut down now. Tomorrow is a busy day, I may not get back on the Montage until late afternoon - but I propose to start by testing it first on the headphones, then plugging the Rockits back in and testing that (leave for at least 30 minutes). Hopefully you'll read this before then, and I would be grateful to have your advice. Thanks and stay well ...

Somewhere in all of that you almost did what I asked. Seems your MONTAGE is fine.

Hello BM - up early to try again. First tried with just the headphones - first strike, instant response, as yesterday. Fine. Re-connected the KRK Rokit G3 6 powered studio monitors and switched them on. First strike - nothing. Second strike produced a sort of reverb effect. Third strike produced the correct sound. So it would appear the Rokit 6s are the problem. Is this known anywhere else, do you know? Is Yamaha aware of it?

I then re-connected the MIDI and A/D inputs for the Tyros, and everything worked normally. I then left it all alone for 30 minutes. The Rokits had turned themselves off - everything else was on. First strike, the Rokits switched on, but no sound from them, but there was the correct sound in the headphones. Second strike, a sort of reverb effect from the Rokits but the headphones produced the correct sound again. Third strike and both the Rokits and the headphones produced the correct sound.

This seems to confirm that there is an issue with the KRK Rokit G3 6s when used with the Montage 7. My worry now is, could that be harmful?

Thanks for your guidance in isolating the problem! Now, what should I do about it, or is there nothing that can be done? Stay well ...

If you take the montage out of the picture and connect the tyros to your Rokits do you get the same behaviour?

Apparently the Rokit speakers need 50db to wake them up...

https://www.gearslutz.com/board/newbie-audio-engineering-production-question-zone/1080485-krk-rokit-6-sleep-function-pain.html

Sean - Thanks ! I can't believe such a dumb feature is not only intended, but built into the Rokits! Nothing in the blurb. Not only that, but it takes a keystrike to switch them back on, with no sound out at all. Nothing wrong with them once you've got them started - but this auto-shutdown ecospeak nonsense should be optional, not mandatory. I now know where the problem lies - as I said, it doesn't bother me, just baffles me that supposedly intelligent sound engineers would consider such a piffling gesture at the risk of upsetting customers and losing sales. I'll bet not a single person has ever bought them because they shut down without permission.