多实例场景下，其中一个实例虚机发生故障实例下线再上线后，server列表中一直没有这个实例ip, 但一段时间后恢复

场景说明：
1.实例所在虚机发生故障，实例的状态转变为不可用；
2.一段时间后实例所在虚机恢复正常，2-3min后该实例服务变为可用；
3.实例恢复正常后，server列表中一直没有这个实例；
4.大约半小时左右后，恢复正常。

什么原因会导致这种问题

No file, test, or entry point is named. Start by tracing the service registration and discovery lifecycle across the reported failure, recovery, and server-list delay, then compare heartbeat and refresh timing. Done means identifying the cause of the delayed reappearance and documenting or validating the expected recovery behavior.

Written by the indexing model from the issue text.