Hello ,
First of all , you are missing the secondary FAB port from secondary Node which should be " ge-5/0/7 " .
Secondly the secondary FAB link "ge-0/0/7" and ge-5/0/7" connecting switch port on CISCO should be in different VLAN as a best practice ( With Jumo Frames enabled ) . Thats why we are getting the errors as the FAB probs are getting confused between the Primary and secondary FAB link .
And also this should be in same VLAN as of other revenue ports .
Now regarding your Failback issue , it seems to be something that need to be checked why it takes almost 30 mins to failback and It may be out of scop of the device ( Maybe the switch might also have causing this ) but they need to identify the issue so that we can proceed . Did the support say if this is a supported setup or not ?