SFOS 19 LACP not coming up to Aruba CX8320 Switch

Hi All, Hoping someone has a fix or knows the issue.

EU has a new XGS2100 with a 4port 10Gb card to replace an SG210 which is used for a secure dept internally. There is a functioning 2 port LACP interface to a Multi-Chassis LAG on 2 x Aruba CX 8320 switches. Swapped it over to the new configured LAG on the XGS2100 and it does not come up.. The 2 ports associated come up on the 8320 but the LAG does not become active and is unreachable.

The config on both the core 8320's is

interface lag 51 multi-chassis

    no shutdown

    description TESTING LINK TO XGS2100

    no routing

    vlan trunk native 1

    vlan trunk allowed all

    lacp mode active

    spanning-tree loop-guard

int 1/1/40

    no shut

    lag 51

The LACP config on the Sophos XGS2100 is

Thanks in advance...