We had a mikrotik to mikrotik backhaul link in operation for a few years, and it worked fine with LDP protocol between these two routers. We replaced the wireless link in between with a ubiquiti link instead (using an available ethernet port on each routerboard instead of the wifi cards), not changing any other configuration on the routers, but now the LDP neighbors keep flapping on and off between these two routers now, No changes in OSPF link states or anything. The funny thing is that on the other side of each of these routers identical ubiquiti configurations/links are working fine.

Mikrotik ->ubi->Mikrotik ->ubi -> Mikrotik -> ubi -> Mikrotik

The 2nd router will show just a "D" for its neighbor but the 3rd router it just disappears off the list.

Above example the LDP between the 2 middle mikrotiks the LDP is unstable. This is only one leg of our network, our other leg also has the exact configurations as well and works fine. The only real difference is one of the boards is an RB600 and its the only one we have in our network. If I set the LDP neighbor force targeted hello between the routers its also stable, it just doesnt work dynamically anymore?? Anyone have any ideas??? Been beating my head on the wall with this one for a week.

If LDP adjacency is maintained fine with targeted hellos, I would say that your link is having trouble forwarding multicast packets (LDP hellos). You can check that with sniffer.

This was my first guess, OSPF doesnt work without NBMA turned on too. Ive examined the configuration of this link to our other identical links and found no differences so Im lost as to why it sometimes does pass multicast and other times it doesnt.

try to set

hello-interval=3s hold-time=20s on ldp interfaces.

would be helpful if ldp neighbors have adjacency time like ospf neighbors ... and state changes too.