This issue has been fixed with Ableton Live update 12.4
Issue
Using Ableton Live 12.3, the VST3 integration that allows SSL 360 (and the controllers) to follow the order of tracks in Ableton Live is broken. If you re-order tracks in the session, you will see that the numbers and order of tracks do not correctly update in the SSL 360 Plug-in Mixer.
This affects UC1 and UF1/UF8 controllers (when set to control the Plug-in Mixer).
It does not affect UF1/UF8 if they are set to the Ableton Live (MCU) layer.
Our assessment is that this bug is being caused by Ableton Live and not SSL 360. This bug has been reported to Ableton for their attention.
We would encourage you to also raise a support ticket regarding this issue with Ableton via their support site, to increase the chances of it being looked at - https://help.ableton.com/hc/en-us/requests/new?ticket_form_id=127269
Workaround
The only way to workaround this issue is to use an earlier version of Live. For instance, Live 12.2 does not have this bug.
You can find previous versions of Live here - https://www.ableton.com/en/download/archive/