question

When using collision detection in A*, the travelers allocate and release nodes as they travel along their path. You can see these allocations if you check the "Show Allocations" box on the Visual tab of A* navigator's properties.

If a traveler has allocated a node, and a second traveler tries to allocate that node, a collision occurs. There is some default logic that attempts to resolve the collision. One of the options that can happen is that the second traveler will wait for the first to leave. If two or more travelers are waiting, and none can move unless another moves, then that is a deadlock, and that's what's happening.

To avoid deadlock, you usually need to find a way to avoid the deadlock situation. Sometimes, you can reduce the number of travelers. Sometimes, you can give travel tasks that generally won't cause a deadlock situation. When you attach a Task Executer to the A* navigator, that traveler gets a trigger called On A Star Block. You can also use this trigger to give a new task sequence when a collision occurs, one that gets out of the deadlock situation.

As far as the Link Parity error, you would need to post a model in order for us to debug that.