Can you try increasing the statusTimeout in distsearch.conf on the DMC will give the searchPeers more slack as the DMC tries to get each Peers info, which in turn will result in less peers showing up as "Down" in /services/search/distributed/peers/.
statusTimeout = <int, in seconds> * Set connection timeout when gathering a search peer's basic info (/services/server/info). * Note: Read/write timeouts are automatically set to twice this value. * Defaults to 10.
You can do this from Setting >>Distributed search >>Distributed search>>Timeout settings and changing the Status timeout (in seconds) from default value 10 to something larger considering your environment.