There's two secenarios in which this can happen: 1) If we're viewing a subsite homepage, which also happens to have one of the fields that this module will follow to find a subsite homepage. 2) If one of the default hook implementations follows a field to find a subsite homepage, and then a subsequent hook finds a field on the subsite homepage to follow. So we need to fix this as follows: 1) Make SubsiteService::isSubsiteType() public so we can call it from hooks. 2) Check if the node we start on is a subsite homepage. If it is, return early. 3) In each alter hook, check if the passed node is a subsite homepage. If it is, don't do anything more.