Found this post on Tesla Forums from a couple days ago. Tesla service confirmed he was rolled back to 8.3 due to issues with 12.5 and 8.3 is the latest available for his build (see text message quote below from service). Still not clear which combination of factors are leading to some M3s being held on 8.3 but this clearly isn't just regular upgrade cycles taking time to get around to everyone.
FULL POST:
Software 2020.12.5 failed and now not available
Submitted by funkiegh on April 30, 2020
My 2020 model M3 AWD LR received in March with 2019 FW was upgraded to 2020.8.3 on 1st April; so far so amazing!.. However on 15th April a friend told me he'd just received 2020.12.5 with the new dashcam viewer - identical car (except for the colour) and delivered on the same day as mine. So I waited patiently for my turn - keen to get the on-board Dashcam / Sentry viewer,.. and waited for a week before contacting the UK support line. When I did, they told me it had been pushed out to me on 15th April but had failed, although I'd had no indication of the attempt or the failure. When I asked them to try again I was told the latest version available to me was 8.3 which I already have - so they told me to raise a service request, which I duly did. The next day I received a text message on my phone:
"Hi Mike your Model 3 is on the latest update we can deploy. There have been some issues with 2020.12.5 hence the rollback. Please wait until this update becomes available shortly. Please note we will not update firmware at customer request we will only push firmware if there has been an issue with a previous install or it is required to fix a issue with the car. We will cancel your appointment thank you."
Does anyone understand the reason for this or had a similar experience? As far as I can tell (Teslafi & Stats app) a vast majority of the fleet (>50%) has 12.5 with 12.6 a close second.. 8.3 is around 8%. Any advice?