[Samba] isc-dhcp-server issues on samba 4.17

[Carlos Jesus]

Hello everybody!
I'm having an issue that I'm not really sure it's samba related. Still,
here it goes to see if anyone has seen this before.
I have 2 DCs debian based that I recently upgraded from Buster to Bullseye.
One is virtual another is physical. Both running bind, and dns-dyn-updates.
dhcp in failover mode "split 128".
In parallel to the "Buster upgrade", I upgraded samba from 4.13 self
compiled to 4.16 bullseye-backports (following Rowland's suggestion, I
created a 3rd DC, then removed/installed/re-joined each DC at a time). It
all went rather well with the usual minor glitches.
In the mean time, 4.17 appeared in the backports so, I upgraded the
physical DC. And now comes my issue.
On this DC, isc-dhcp-server wont start, complaining about:
isc-dhcp-server[1453137]: /usr/sbin/dhcpd: error while loading shared
libraries: libisc-export.so.1100: cannot open shared object file: No such
file or directory
This is of course true, since bind (9.16.27) uses libisc-export.so.1105
which is there.
I've checked the configuration against the other DC (where everything
works) and they are similar. Another weird fact is that removing
isc-dhcp-server (and then apt autoremove) and then reinstalling
isc-dhcp-server makes the server work. But only until the next reboot or
systemctl restart.
Due to this last fact, I'm not really sure, where in the upgrade process,
the dhcp server stopped working.

What I did:
1) tried with a basic dhcp.conf (not failover)
2) checked dhcp and bind configuration against samba wiki and the other DC
3) changed dns backend to samba_internal and back
4) reinstalled isc-dhcp and bind9 (results in the above behaviour)
5) Disabled apparmor

What i didn't do
1) create a link for libisc-export. That would maybe solve it but its a
c****y solution.
2) remove, reinstall and re-join

I've found something that seems to be related in the debian bug reports
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=995242
Not sure it's the same issue.

Any clues? Again, not sure this is samba related or not, but truth is
everything works on the virtual DC with samba 4.16.

Best regards,
CJ