strace shows that a mount is failing, but I have no idea why, given the path exists…
1917811 clone(child_stack=0, flags=CLONE_NEWNS|CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWPID|CLONE_NEWNET|SIGCHLD) = 1917839
1917839 close(12 <unfinished ...>
1917811 open("/proc/1917839/ns/mnt", O_RDONLY|O_CLOEXEC <unfinished ...>
1917839 <... close resumed> ) = 0
1917839 prctl(PR_SET_PDEATHSIG, SIGKILL <unfinished ...>
1917839 <... prctl resumed> ) = 0
1917811 open("/proc/1917839/ns/pid", O_RDONLY|O_CLOEXEC <unfinished ...>
1917839 getppid( <unfinished ...>
1917839 <... getppid resumed> ) = 0
1917811 open("/proc/1917839/ns/uts", O_RDONLY|O_CLOEXEC <unfinished ...>
1917839 getuid( <unfinished ...>
1917839 <... getuid resumed> ) = 0
1917811 open("/proc/1917839/ns/ipc", O_RDONLY|O_CLOEXEC <unfinished ...>
1917839 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
1917839 read(11, <unfinished ...>
1917811 open("/proc/1917839/ns/net", O_RDONLY|O_CLOEXEC) = 19
1917839 <... read resumed> "\0\0\0\0", 4) = 4
1917839 write(11, "\1\0\0\0", 4 <unfinished ...>
1917839 <... write resumed> ) = 4
1917839 read(11, <unfinished ...>
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 write(11, "1917839", 7) = 7
1917811 open("/proc/1917839/ns/net", O_RDONLY|O_CLOEXEC) = 11
1917839 <... read resumed> "\2\0\0\0", 4) = 4
1917839 access("/var/snap/lxd/common/lxd/containers", X_OK) = 0
1917839 write(11, "\3\0\0\0", 4) = 4
1917839 read(11, <unfinished ...>
1917839 <... read resumed> "\4\0\0\0", 4) = 4
1917839 unshare(CLONE_NEWCGROUP) = 0
1917839 open("/proc/self/mountinfo", O_RDONLY|O_CLOEXEC) = 12
1917839 memfd_create(".lxc_mountinfo", MFD_CLOEXEC) = 15
1917839 sendfile(15, 12, NULL, 2147479552) = 11033
1917839 close(12) = 0
1917839 lseek(15, 0, SEEK_SET) = 0
1917839 fcntl(15, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE)
1917839 fstat(15, {st_dev=makedev(0, 5), st_ino=19205626, st_mode=S_IFREG|0777, st_nlink=0, st_uid=0, st_gid=0, st_blksize=4096, st_blocks=24, st_size=11033, st_atime=2019/03/26-15:26:36.935141750, st_mtime=2019/03/26-15:26:36.935141750, st_ctime=2019/03/26-15:26:36.935141750}) = 0
1917839 read(15, "217 216 7:0 / / ro,nodev,relatime master:34 - squashfs /dev/loop0 ro\n218 217 0:6 / /dev rw,nosuid master:3 - devtmpfs devtmpfs rw,size=131869172k,nr_inodes=32967293,mode=755\n219 218 0:21 / /dev/shm rw,nosuid,nodev master:4 - tmpfs tmpfs rw\n220 218 0:22 / /dev/pts rw,nosuid,noexec,relatime master:5 - devpts devpts rw,gid=5,mode=620,ptmxmode=000\n221 220 0:47 / /dev/pts rw,relatime - devpts devpts rw,gid=5,mode=620,ptmxmode=666\n222 218 0:18 / /dev/mqueue rw,relatime master:27 - mqueue mqueue rw\n223 218 0:40 / /dev/hugepages rw,relatime master:28 - hugetlbfs hugetlbfs rw,pagesize=2M\n224 218 0:47 /ptmx /dev/ptmx rw,relatime - devpts devpts rw,gid=5,mode=620,ptmxmode=666\n225 217 253:3 / /home rw,relatime master:31 - ext4 /dev/mapper/vg01-home rw\n226 225 253:5 /lib/one /home/oneadmin rw,relatime master:32 - ext4 /dev/mapper/vg01-var rw\n227 226 7:6 / /home/oneadmin/datastores/100/743/mapper/disk.1 ro,relatime master:49 - iso9660 /dev/loop6 ro,nojoliet,check=s,map=n,blocksize=2048\n228 226 7:7 /"..., 4096) = 4096
1917839 mount(NULL, "/var/snap/lxd/common/shmounts", NULL, MS_SLAVE, NULL) = 0
1917839 mount(NULL, "/var/snap/lxd/common/shmounts/lxcfs", NULL, MS_SLAVE, NULL) = 0
1917839 read(15, "ed:45 - tmpfs tmpfs rw,size=100k,mode=711\n258 254 43:2304 / /var/snap/lxd/common/lxd/storage-pools/default/containers/one-743/rootfs rw,relatime master:46 - ext4 /dev/nbd9 rw\n259 254 43:2561 / /var/snap/lxd/common/lxd/storage-pools/default/containers/one-744/rootfs rw,relatime master:53 - xfs /dev/nbd10p1 rw,attr2,inode64,noquota\n260 254 0:55 / /var/snap/lxd/common/lxd/devlxd rw,relatime - tmpfs tmpfs rw,size=100k,mode=755\n261 254 252:16 / /var/snap/lxd/common/lxd/storage-pools/default/containers/c1 rw,relatime - ext4 /dev/rbd1 rw,discard,stripe=1024\n262 254 7:6 / /var/snap/lxd/common/lxd/devices/one-743/disk.context.context ro,relatime master:49 - iso9660 /dev/loop6 ro,nojoliet,check=s,map=n,blocksize=2048\n263 254 252:0 / /var/snap/lxd/common/lxd/storage-pools/default/containers/one-743 rw,relatime - ext4 /dev/rbd0 rw,discard,stripe=1024\n264 217 253:5 /lib/snapd /var/lib/snapd rw,relatime master:32 - ext4 /dev/mapper/vg01-var rw\n265 264 7:1 / /var/lib/snapd/snap/lxd/10343 ro,nodev,rel"..., 4096) = 4096
1917839 mount(NULL, "/var/snap/lxd/common/shmounts/containers", NULL, MS_SLAVE, NULL) = 0
1917839 read(15, "419 325 0:42 / /var/lib/snapd/hostfs/mnt/auto/app rw,noatime master:37 - nfs admin1.vip.riskiq:/app rw,vers=3,rsize=32768,wsize=32768,namlen=255,soft,proto=tcp,timeo=3,retrans=5,sec=sys,mountaddr=10.8.1.4,mountvers=3,mountport=59321,mountproto=udp,local_lock=none,addr=10.8.1.4\n422 268 0:6 / /var/lib/snapd/hostfs/dev rw,nosuid master:3 - devtmpfs devtmpfs rw,size=131869172k,nr_inodes=32967293,mode=755\n423 268 0:4 / /var/lib/snapd/hostfs/proc rw,nosuid,nodev,noexec,relatime master:6 - proc proc rw\n424 268 0:20 / /var/lib/snapd/hostfs/sys rw,nosuid,nodev,noexec,relatime master:7 - sysfs sysfs rw\n425 424 0:54 / /var/lib/snapd/hostfs/sys/fs/fuse/connections rw,relatime master:274 - fusectl fusectl rw\n426 217 253:5 /tmp /var/tmp rw,relatime master:32 - ext4 /dev/mapper/vg01-var rw\n427 217 253:1 /lib/modules /lib/modules rw,relatime master:2 - ext4 /dev/mapper/vg01-usr rw\n428 217 253:1 /src /usr/src rw,relatime master:2 - ext4 /dev/mapper/vg01-usr rw\n429 217 253:5 /log /var/log rw,relatime ma"..., 4096) = 2841
1917839 mount(NULL, "/media", NULL, MS_SLAVE, NULL) = 0
1917839 read(15, "", 4096) = 0
1917839 close(15) = 0
1917839 access("/var/snap/lxd/common/lxc/", F_OK) = 0
1917839 mount("/var/snap/lxd/common/lxd/containers/one-743/rootfs", "/var/snap/lxd/common/lxc/", 0x7f88fd51cb21, MS_BIND|MS_REC, NULL) = -1 ENOENT (No such file or directory)
1917839 write(7, "lxc one-743 20190326222636.937 ERROR dir - storage/dir.c:dir_mount:198 - No such file or directory - Failed to mount \"/var/snap/lxd/common/lxd/containers/one-743/rootfs\" on \"/var/snap/lxd/common/lxc/\"\n", 204) = 204
1917839 write(7, "lxc one-743 20190326222636.938 ERROR conf - conf.c:lxc_mount_rootfs:1351 - Failed to mount rootfs \"/var/snap/lxd/common/lxd/containers/one-743/rootfs\" onto \"/var/snap/lxd/common/lxc/\" with options \"(null)\"\n", 209) = 209
1917839 write(7, "lxc one-743 20190326222636.938 ERROR conf - conf.c:lxc_setup_rootfs_prepare_root:3498 - Failed to setup rootfs for\n", 118) = 118
1917839 write(7, "lxc one-743 20190326222636.938 ERROR conf - conf.c:lxc_setup:3551 - Failed to setup rootfs\n", 94) = 94
1917839 close(14) = 0
1917839 close(13) = 0
1917839 write(7, "lxc one-743 20190326222636.938 ERROR start - start.c:do_start:1282 - Failed to setup container \"one-743\"\n", 108) = 108
1917839 write(11, "\377\377\377\377", 4) = 4
1917839 exit_group(-1) = ?
1917839 +++ exited with 255 +++
1917811 kill(1917839, SIGKILL <unfinished ...>
1917811 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 255}], 0, NULL) = 1917839
1917811 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=1917839, si_uid=0, si_status=255, si_utime=0, si_stime=0} ---