When you add a host to a pool, most things are taken care of for you.

One exception is Network Names.

Be sure to rename networks to the names used in the pool before joining the new host!

On pool master:

xe network-list

On host to be joined, configure the same labels as on the pool master:

xe network-list

xe network-param-set name-label=Management uuid=<UUID-xenbr0>
xe network-param-set name-label=GuestPublic uuid=<UUID-xenbr1>
xe network-param-set name-label=BlockStorage uuid=<UUID-xenbr2>
xe network-param-set name-label=FileStorage uuid=<UUID-xenbr3>

Then join the new host.