Running "dmesg", I see the following error:

[ 2403.606334] audit: type=1400 audit(1669997382.596:431): apparmor="DENIED" operation="mount" info="failed flags match" error=-13 profile="lxc-container-default-cgns" name="/" pid=7607 comm="(ionclean)" flags="rw, rslave"

[ 2847.490460] audit: type=1400 audit(1669997826.464:441): apparmor="DENIED" operation="mount" info="failed type match" error=-13 profile="lxc-container-default-cgns" name="/tmp/efs/" pid=8093 comm="mount.nfs4" fstype="nfs4" srcname="10.115.12.239:/"

And noticed "lxc" is listed in the error. That stands for Linux Container. Which leads me to believe the EFS mount problems are, perhaps, related to how Databricks sets up its runtime using LXC.

Must be related to LXC permissions, somehow.