Hello.
in the docs talking about stacks (exception of MS390), nothing is mentionned about a specific order for reboot.
at the creation of the stack MERAKI just say to power-up all together, but nothing regarding a reboot.
this week for a test, I had to physically reboot (unplug power cables) a big stack of 6xMS250-48FP with double power-supply, and what I can tell you is the order may be but more the convergence time.
I tried first to re-power the first one on top of the rack, wait 30s and then plug the rest in the vertical order 2 to 6.
I thought it was ok when I saw on front view the 1st switch getting Fixed White LED, but few second after it became fixed orange like all others. I waited 3 minutes and nothing change the first one did not came back to fixed white.
So I decided to unplug and replug again but this time in a specific order. I powered-up the first switch, and after 30s the last switch of the stack. My idea was to define the ring in that way and force the 1st switch to become the Active 5master) one.
But this time I waited these two to be stable with the fixed white LED. and then only after I plugged switches 2, 3, 4, and 5.
it took a while for the 4 in the middle to become fixed white, but a least the first and the last remained stable white!
once all were white, I then plugged my second uplink part of a LAG I configured between the first and the last switches, to the core network (MS425-16).
everything looked fine, but I noticed a shift in the dashboard showing well all the switch but curiously with several ports on several switches, denying the power to connected devices (orange-brown port status); but after 2-3min it was fine.
Personnally I will continue to use this method for physical reboot, but it supposed to have 'middle switches' out of power for initial boot of first and last switch.
Remotly via the dashboard I would recommend to click one by one REBOOT from 1st switch to last one in the order.
hoping it can help you