Phones rebooting mid-call "Uploading 1 of 1 core files"

We have been receiving reports from users that their Polycom VVX 450 desk phones are rebooting, sometimes in the middle of a call (as just happened to me) and doing some kind of file upload. The message on the screen shows, among other things, "Uploading 1 of 1 core files". Here's a video that I started around 20 seconds into the process: https://youtu.be/Gv8HUxOCH_c

We bought the phones around 12 months ago from RingCentral.

We have had a ticket open with RingCentral Support since last Thursday, and they have made no progress whatsoever, so I decided to turn to the Community to see if anyone had any idea what was going on, and more importantly, how to prevent it from happening.

Any help would be greatly appreciated.