What is EIGRP Stuck in Active situation?

When Query and Reply is generated?

If the topology table has only one successor and when the best path (successor route) goes down it will immediately send the Query to all the interface where EIGRP is enabled.When positive reply comes it will use that path as successor and removes the old successor.If there is feasible successor in Topological table it will not generate query,Instead it will wait up to 15 seconds(convergence time) and use the feasible successor as successor and use that path for forwarding packet.

When SIA Query is generated?

SIA means stuck in active.It is generated after 90 seconds of Query message.If reply is not received up to 90 seconds it will send Stuck in Active Query to neighbor router.The reason for sending is to stop breaking neighbourship without valid reason.As neighbor router also send query to its neighbor in chain it may also wait for the reply.So instead of breaking neighborship it will wait up to 180 seconds for SIA reply.If SIA reply came within 180 seconds it will not break neighborship otherwise it will break the neighborship.