We had upgraded to v7.10 on some of our edge routers recently, and it looks like the ldp interface shows passive status if either of the router is on version 6. For example, edge router "A" was on v6 which had mpls tunnels to router "B" and "C" which are on 7.10. We found that router "C" wouldn't be stable after the upgrade and router "B" was showing the ldp interface to "C" as passive.
We had to downgrade the firmware on both "B" and "C" to make everything stable (This is arm architecture).

Also, noticed this same issue on CCR1036 where one edge router is on v7 and other on v6. We lose access to the router on v6 when the mpls to that router is enable on other router. However, customer traffic continues to flow. This is with firmware v7.8. No reply from mikrotik support team yet.