Tried a few things and below are the results. Seems maybe the zfs setup is bugged?
root@prox2:~# pct mount 102
mounting container failed
cannot open directory //rpool/data/subvol-102-disk-1: No such file or directory
root@prox2:~# pct mount 102^C
root@prox2:~# ^C
root@prox2:~# zfs list
NAME USED AVAIL REFER MOUNTPOINT
rootpool 13.5G 94.0G 96K /rootpool
rootpool/ROOT 4.73G 94.0G 96K /rootpool/ROOT
rootpool/ROOT/pve-1 4.73G 94.0G 4.73G /
rootpool/data 96K 94.0G 96K /rootpool/data
rootpool/swap 8.50G 95.9G 6.61G -
rpool 1.72T 1.79T 96K /rpool
rpool/data 1.72T 1.79T 112K /rpool/data
rpool/data/subvol-102-disk-1 291G 72.4G 278G /rpool/data/subvol-102-disk-1
rpool/data/subvol-104-disk-1 421M 1.59G 421M /rpool/data/subvol-104-disk-1
rpool/data/subvol-105-disk-1 5.36G 14.6G 5.36G /rpool/data/subvol-105-disk-1
rpool/data/subvol-107-disk-1 2.46G 2.55G 2.45G /rpool/data/subvol-107-disk-1
rpool/data/subvol-108-disk-1 1.06G 970M 1.05G /rpool/data/subvol-108-disk-1
rpool/data/subvol-109-disk-1 1.12G 898M 1.12G /rpool/data/subvol-109-disk-1
rpool/data/subvol-110-disk-1 4.22G 1.78G 4.22G /rpool/data/subvol-110-disk-1
rpool/data/subvol-112-disk-0 537M 1.48G 537M /rpool/data/subvol-112-disk-0
rpool/data/subvol-112-disk-2 544G 56.3G 544G /rpool/data/subvol-112-disk-2
rpool/data/vm-100-disk-1 25.1G 1.79T 25.1G -
rpool/data/vm-101-disk-1 14.0G 1.79T 14.0G -
rpool/data/vm-103-disk-1 132M 1.79T 132M -
rpool/data/vm-106-disk-1 375G 1.79T 375G -
rpool/data/vm-111-disk-0 6.82G 1.79T 6.82G -
rpool/data/vm-113-disk-0 13.6G 1.79T 13.6G -
rpool/data/vm-113-disk-1 212G 1.79T 210G -
rpool/data/vm-115-disk-0 261G 1.79T 261G -
root@prox2:~# pct fsck 102
unable to run fsck for 'local-zfs:subvol-102-disk-1' (format == subvol)
root@prox2:~# lxc-start -n 102 0F 0l DEBUG -o /tmp/lxc-102.log
lxc-start: 102: lxccontainer.c: wait_on_daemonized_start: 856 No such file or directory - Failed to receive the container state
lxc-start: 102: tools/lxc_start.c: main: 330 The container failed to start
lxc-start: 102: tools/lxc_start.c: main: 333 To get more details, run the container in foreground mode
lxc-start: 102: tools/lxc_start.c: main: 336 Additional information can be obtained by setting the --logfile and --logpriority options
lxc-start 102 20190718170159.256 ERROR conf - conf.c:run_buffer:335 - Script exited with status 2
lxc-start 102 20190718170159.256 ERROR start - start.c:lxc_init:861 - Failed to run lxc.hook.pre-start for container "102"
lxc-start 102 20190718170159.256 ERROR start - start.c:__lxc_start:1944 - Failed to initialize container "102"
lxc-start 102 20190718170159.256 ERROR lxccontainer - lxccontainer.c:wait_on_daemonized_start:856 - No such file or directory - Failed to receive the container state
lxc-start 102 20190718170159.256 ERROR lxc_start - tools/lxc_start.c:main:330 - The container failed to start
lxc-start 102 20190718170159.256 ERROR lxc_start - tools/lxc_start.c:main:333 - To get more details, run the container in foreground mode
lxc-start 102 20190718170159.256 ERROR lxc_start - tools/lxc_start.c:main:336 - Additional information can be obtained by setting the --logfile and --logpriority options
root@prox2:~# pct mount 102
mounting container failed
cannot open directory //rpool/data/subvol-102-disk-1: No such file or directory
root@prox2:~# pct mount 102^C
root@prox2:~# ^C
root@prox2:~# zfs list
NAME USED AVAIL REFER MOUNTPOINT
rootpool 13.5G 94.0G 96K /rootpool
rootpool/ROOT 4.73G 94.0G 96K /rootpool/ROOT
rootpool/ROOT/pve-1 4.73G 94.0G 4.73G /
rootpool/data 96K 94.0G 96K /rootpool/data
rootpool/swap 8.50G 95.9G 6.61G -
rpool 1.72T 1.79T 96K /rpool
rpool/data 1.72T 1.79T 112K /rpool/data
rpool/data/subvol-102-disk-1 291G 72.4G 278G /rpool/data/subvol-102-disk-1
rpool/data/subvol-104-disk-1 421M 1.59G 421M /rpool/data/subvol-104-disk-1
rpool/data/subvol-105-disk-1 5.36G 14.6G 5.36G /rpool/data/subvol-105-disk-1
rpool/data/subvol-107-disk-1 2.46G 2.55G 2.45G /rpool/data/subvol-107-disk-1
rpool/data/subvol-108-disk-1 1.06G 970M 1.05G /rpool/data/subvol-108-disk-1
rpool/data/subvol-109-disk-1 1.12G 898M 1.12G /rpool/data/subvol-109-disk-1
rpool/data/subvol-110-disk-1 4.22G 1.78G 4.22G /rpool/data/subvol-110-disk-1
rpool/data/subvol-112-disk-0 537M 1.48G 537M /rpool/data/subvol-112-disk-0
rpool/data/subvol-112-disk-2 544G 56.3G 544G /rpool/data/subvol-112-disk-2
rpool/data/vm-100-disk-1 25.1G 1.79T 25.1G -
rpool/data/vm-101-disk-1 14.0G 1.79T 14.0G -
rpool/data/vm-103-disk-1 132M 1.79T 132M -
rpool/data/vm-106-disk-1 375G 1.79T 375G -
rpool/data/vm-111-disk-0 6.82G 1.79T 6.82G -
rpool/data/vm-113-disk-0 13.6G 1.79T 13.6G -
rpool/data/vm-113-disk-1 212G 1.79T 210G -
rpool/data/vm-115-disk-0 261G 1.79T 261G -
root@prox2:~# pct fsck 102
unable to run fsck for 'local-zfs:subvol-102-disk-1' (format == subvol)
root@prox2:~# lxc-start -n 102 0F 0l DEBUG -o /tmp/lxc-102.log
lxc-start: 102: lxccontainer.c: wait_on_daemonized_start: 856 No such file or directory - Failed to receive the container state
lxc-start: 102: tools/lxc_start.c: main: 330 The container failed to start
lxc-start: 102: tools/lxc_start.c: main: 333 To get more details, run the container in foreground mode
lxc-start: 102: tools/lxc_start.c: main: 336 Additional information can be obtained by setting the --logfile and --logpriority options
lxc-start 102 20190718170159.256 ERROR conf - conf.c:run_buffer:335 - Script exited with status 2
lxc-start 102 20190718170159.256 ERROR start - start.c:lxc_init:861 - Failed to run lxc.hook.pre-start for container "102"
lxc-start 102 20190718170159.256 ERROR start - start.c:__lxc_start:1944 - Failed to initialize container "102"
lxc-start 102 20190718170159.256 ERROR lxccontainer - lxccontainer.c:wait_on_daemonized_start:856 - No such file or directory - Failed to receive the container state
lxc-start 102 20190718170159.256 ERROR lxc_start - tools/lxc_start.c:main:330 - The container failed to start
lxc-start 102 20190718170159.256 ERROR lxc_start - tools/lxc_start.c:main:333 - To get more details, run the container in foreground mode
lxc-start 102 20190718170159.256 ERROR lxc_start - tools/lxc_start.c:main:336 - Additional information can be obtained by setting the --logfile and --logpriority options