I’ve noticed that on the switches that have upgraded successfully. Problem is, I have two switches (so far) that have refused to upgrade. I’ve tried about half dozen times each; one is my test switch and the other I installed last week and recently upgraded to 2.15 from 2.08. I have 18 more installed VZM31-SNs to upgrade (and about half a dozen left to install & upgrade).
Edit: one of the two switches did eventually update, still no dice on my test switch though 
I’ve tried another ~half dozen times in total since this post (~dozen total).
Update 2024-05-10 - I’ve successfully updated 24 of 25 switches. My test switch is the only one being left behind (reports successful every time, but never actually upgrades). I think I’m going to be opening a ticket with Support for it next week. I have a second (not installed) switch that I need to open a case for anyway.
Update 2024-05-15 - A couple more freshly installed switches successfully upgraded. Ticket opened with Inovelli (2024-05-13) and waiting to hear back regarding the switch that will not upgrade OTA.