Yes, I also have this strange behaviour on my zenfone 8.
I'm in France with SFR as provider.
Sometimes it does not deregister for several days, Sometimes after few minutes in standby, when I reactivate the screen, the vowifi icon is not present.
Most of the time, it reapears within few seconds, Sometimes, I have to disable and re-enable vowifi.
My provider is not faulty as it never deregisters on my pixel 5.
This minor issue together with the late security patch es are my only minor complaintes on the zenfone 8.
Appart from this, this is perfectly running under Android 12,great performance, great battery life, good picture quality with gcam, perfect size and weight. All by all, really happy for the moment.
Hope it will Last and that no ramdump will occur on my phone 😉