samba-tool throws a Segmentation fault for some operations since 4.6.0, e.g. for samba-tool drs showrepl samba-tool ntacl sysvolcheck samba-tool dbcheck Others like samba-tool user list, samba-tool testparm etc. work smoothly.
Seems to be a packaging issue, updating python-tdb to 2.1.9 instead of 2.1.6 helped.