Lately I had this weird problem that people are able to call me, but my phone doesn't ring, neither I get missed call notification. This mostly happens after losing cellular service (going into tunnels, low coverage areas, etc.) and the issue disappears after reboot. It is possible that telephony service somehow disconnect itself from the notification bus thus not delivering notifications?
After running dmesg I was able to find something like this:
phablet@ubuntu-phablet:~$ dmesg | grep ofono
[ 13.626692] capability: warning: `ofonod' uses 32-bit capabilities (legacy support in use)
[ 4439.324679] audit: type=1400 audit(1716137097.140:664): apparmor="DENIED" operation="open" info="Failed name lookup - disconnected path" error=-13 profile="/usr/lib/telepathy/telepathy-ofono" name="usr/lib/aarch64-linux-gnu/qt5/plugins/sqldrivers" pid=5071 comm="telepathy-ofono" requested_mask="r" denied_mask="r" fsuid=32011 ouid=0