yup!!! the samba version for zentyal 6.2 is 4.7 on ubuntu 18.04 ?? no remember now...
You can force update of samba, but no recommend, the config could broken if only update samba, also other version samba requires other version bind, for config dns, if you haven't never experienced, the best is work on some VM.
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Recently I upgrade a server ubuntu 18.04 to 20.04, no zentyal, (this server work samba-ad-dc, bind9, isc-dhcp, webmin and other utilities) at moment update samba I installed 4.11 and bind 9.16.1, I regenerated the dc using smbconfig file bkp, also I kept all files...for end all upgrade installed ok and all services perfect running...