Ext4-fs error during "docker stack deploy"(?)


I have a couple of VirtualBox VMs, set up by Vagrant (debian/contrib-stretch64 9.5). Those VMs are running a Docker stack (in general one container per VM) for testing purposes. VirtualBox is 5.2.18, Docker version 18.06.1-ce, build e68fc7a

Every now and then, it appears to happen right during or after “docker stack deploy”, one of the VMs seems to run into an error condition:
EXT4-fs error (device sda1): ext4_find_entry:nnnn: inode #nnnnnn: comm sshd: reading directory lblock 0

It’s not always “sshd”, but, at least, “sssd_be” as well.

The partition is remounted read-only, I cannot login, only shutdown the VM and reboot. I couldn’t find anything inside the logs. Sometimes I even need to recreate the affected VM.

Unfortunately, since we have about 12 VMs, it happens rather often to one or another of the VMs. Not the same every time though-

Any idea what might be causing this? Debian? Docker? VirtualBox? And what could I do prevent it?


PS: See my post in the VirtualBox forum