I did a test upgrade on a MS-120 8ports today from 12.28 to 14.22.
The upgrade took approx. 20 minuttes before it rebooted. After it came up again, it would not contact the cloud and the the trunk interfaces carrying my internet traffic between my COAX modem and firewall did not pass traffic - or at least not the dhcp traffic my firewal was requesting from the cable provider.
All local lan traffic was working and while i was poking around and did a support file request from the switch, the switch rebooted once more (after approx. 10 minuttes uptime) and this time after a reboot, all traffic started to work again.
All necessary ports is open to the correct destinations, so it is not a firewall issue. The issue lies within the switching itself. In my test setup i have 2 trunk ports where one port is connected to a firewall and another port is connected to 3. party switch again connected to a coax cable modem. The firewall get a pulic ip address assigned by dhcp - through the trunk ports - and this was not working well with v. 14.22. As soon as i downgraded to 12.28 is all started working again fine.
I did not spend much time debuging and the only reason i did a test with version 14.22 was because Meraki had auto scheduled firmware upgrade of all my switches to 14.22. Those schedules i have now removed. I also wondered why Meraki would auto schedule upgrades to stable release candidates.
@RVilhelmsen it may well be related to your configuration, I have a site running 14.22 on MS210s without issue and two sites running 14.21 with 355s, 225s, a 220, 210s and four 120s. On the site with the 355s 12.28 had major issues, whereas 14.19-21 have all been good.