I have similar experience here: no core dumps, but after upgrading from
2:4.2.14+dfsg-0+deb8u2 to 2:4.2.14+dfsg-0+deb8u4 I cannot access shares
that have shadow_copy2 vfs module enabled. The rest of the shares work
OK. Downgrading solves the problem.
It may not be a completely isolated issue.
--jtg