Overlayfs goes to tmpfs on RPi4 build

Hi all

I have updated my RPi4 build, keeping the diffconfig of my ruter configuration, that includes several packages and increased root filesystem partition (1024Mb)

I also embedd the configuration in the "files" directory. So build is ok, configuration files are there, but the overlayfs goes to tmpfs so it is not possible to make any persisten configuration (I use squashfs image)

I tried both sysupgrade and a fresh flash of the SD Card, same result

What can I check to fix the problem? Inspect of dmesg or logread does not give any clue, mount says:

/dev/root on /rom type squashfs (ro,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,noatime)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,noatime)
cgroup2 on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noatime)
tmpfs on /tmp/root type tmpfs (rw,noatime,mode=755)
overlayfs:/tmp/root on / type overlay (rw,noatime,lowerdir=/,upperdir=/tmp/root/upper,workdir=/tmp/root/work)
/dev/mmcblk0p1 on /boot type vfat (rw,noatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
tmpfs on /dev type tmpfs (rw,nosuid,relatime,size=512k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,mode=600,ptmxmode=000)
debugfs on /sys/kernel/debug type debugfs (rw,noatime)
none on /sys/fs/bpf type bpf (rw,nosuid,nodev,noexec,noatime,mode=700)

No one can help?