are you sure that your proxmox hosts are both updated to last packages version ?
So funny thing, I just discovered it's only on one node this is happening..
My versions are the same. It only fails on node1. One node2 I can migrate both ways..
root@node1:~# pveversion -v
proxmox-ve: 6.0-2 (running kernel: 5.0.21-3-pve)
pve-manager: 6.0-9 (running version: 6.0-9/508dcee0)
pve-kernel-5.0: 6.0-9
pve-kernel-helper: 6.0-9
pve-kernel-5.0.21-3-pve: 5.0.21-7
pve-kernel-5.0.15-1-pve: 5.0.15-1
ceph-fuse: 12.2.11+dfsg1-2.1+b1
corosync: 3.0.2-pve4
criu: 3.11-3
glusterfs-client: 5.5-3
ksm-control-daemon: 1.3-1
libjs-extjs: 6.0.1-10
libknet1: 1.13-pve1
libpve-access-control: 6.0-2
libpve-apiclient-perl: 3.0-2
libpve-common-perl: 6.0-5
libpve-guest-common-perl: 3.0-1
libpve-http-server-perl: 3.0-3
libpve-storage-perl: 6.0-9
libqb0: 1.0.5-1
lvm2: 2.03.02-pve3
lxc-pve: 3.1.0-65
lxcfs: 3.0.3-pve60
novnc-pve: 1.1.0-1
proxmox-mini-journalreader: 1.1-1
proxmox-widget-toolkit: 2.0-8
pve-cluster: 6.0-7
pve-container: 3.0-7
pve-docs: 6.0-7
pve-edk2-firmware: 2.20190614-1
pve-firewall: 4.0-7
pve-firmware: 3.0-2
pve-ha-manager: 3.0-2
pve-i18n: 2.0-3
pve-qemu-kvm: 4.0.0-7
pve-xtermjs: 3.13.2-1
qemu-server: 6.0-9
smartmontools: 7.0-pve2
spiceterm: 3.1-1
vncterm: 1.6-1
zfsutils-linux: 0.8.2-pve1
root@node2:~# pveversion -v
proxmox-ve: 6.0-2 (running kernel: 5.0.21-3-pve)
pve-manager: 6.0-9 (running version: 6.0-9/508dcee0)
pve-kernel-5.0: 6.0-9
pve-kernel-helper: 6.0-9
pve-kernel-5.0.21-3-pve: 5.0.21-7
pve-kernel-5.0.15-1-pve: 5.0.15-1
ceph-fuse: 12.2.11+dfsg1-2.1+b1
corosync: 3.0.2-pve4
criu: 3.11-3
glusterfs-client: 5.5-3
ksm-control-daemon: 1.3-1
libjs-extjs: 6.0.1-10
libknet1: 1.13-pve1
libpve-access-control: 6.0-2
libpve-apiclient-perl: 3.0-2
libpve-common-perl: 6.0-5
libpve-guest-common-perl: 3.0-1
libpve-http-server-perl: 3.0-3
libpve-storage-perl: 6.0-9
libqb0: 1.0.5-1
lvm2: 2.03.02-pve3
lxc-pve: 3.1.0-65
lxcfs: 3.0.3-pve60
novnc-pve: 1.1.0-1
proxmox-mini-journalreader: 1.1-1
proxmox-widget-toolkit: 2.0-8
pve-cluster: 6.0-7
pve-container: 3.0-7
pve-docs: 6.0-7
pve-edk2-firmware: 2.20190614-1
pve-firewall: 4.0-7
pve-firmware: 3.0-2
pve-ha-manager: 3.0-2
pve-i18n: 2.0-3
pve-qemu-kvm: 4.0.0-7
pve-xtermjs: 3.13.2-1
qemu-server: 6.0-9
smartmontools: 7.0-pve2
spiceterm: 3.1-1
vncterm: 1.6-1
zfsutils-linux: 0.8.2-pve1