[Samba] ldb errors after upgrade, cause?

[Roel van Meer]

Hi!

recently we upgraded a Debian jessie server to Debian buster, with Samba  
being upgraded from 4.5.12 (+dfsg-2+deb9u3) to 4.9.5 (+dfsg-5+deb10u1).

A few hours later we saw these errors in syslog:

    smbd[26024]: [2020/02/03 11:13:13.631613,  0] ../lib/ldb-samba/ldb_wrap.c:79(ldb_wrap_debug)
    smbd[26024]:   ldb: Failure during ltdb_lock_read(): Locking error → Busy
    smbd[26024]: [2020/02/03 11:13:13.631762,  0] ../lib/ldb-samba/ldb_wrap.c:79(ldb_wrap_debug)
    smbd[26024]:   ldb: module samba_dsdb initialization failed : Operations error
    smbd[26024]: [2020/02/03 11:13:13.631828,  0] ../lib/ldb-samba/ldb_wrap.c:79(ldb_wrap_debug)
    smbd[26024]:   ldb: Unable to load modules for /var/lib/samba/private/sam.ldb: Unable to load ltdb cache records for backend 'ldb_tdb backend'

I was wondering if someone knows in which area we have to find a solution.  
Is this resource exhaustion? Or database corruption? Something else?
I did run "samba-tool dbcheck --cross-ncs" afterwards, and this fixed some  
errors, but I'm not sure if that can be related to the ldb errors.

Just wondering if this rings a bell for anyone, with maybe some tips on how  
to proceed from here.

Thanks!

Roel