I'm seeing the same thing. Meraki pushed out 14.45 to 10 of my sites about 2 weeks ago. One device (luckily a new site not deployed yet) is actually stuck bouncing online/offline. After reaching out to support, they said the following:
"Your MX device seems to be having firmware update issues that are resulting in connectivity problems upstream. The MX version on your <network name> network appears to be a deprecated firmware version that is no longer supported."
I was able to downgrade that device, but it was still doing the up/downs, so now they are having me do a factory reset on the device. I can get over there until Monday, so I'll report back here with the results.
If anyone sees different firmware come available I'd appreciate you updating this thread!