Connection loss to Realm server when entity passes through nether portal

When an entity or Mob passes through a specific nether portal on my Realms server, the connection closes for all players on the realm. The error is reported as "Java error: Connection refused." Attempting to log back in will give message of "Realm Closed" After a short time, less than 5 minutes, players can re-enter the game.

Nearby nether portals tested with entities passing through and no connection loss.