We usually take this as a loss, and we naturally take it personally. But we must understand that individuals can have appropriate reasons for moving to another congregation. If members are moving to an unhealthy church that does not preach Jesus as central to the gospel, then we as pastors should be rightly alarmed. As Christians we all need to be reminded that there have always been many different forces at work against the church. In whatever era or age that Christians have lived, there have been plenty of controversies competing with the gospel.
Worship music is a hot button for some.
Spiritual gifts is controversial for others. Some like to debate the Hebrew calendar, as if it is relevant for today. There are many reasons that can cause us not to get along. I suppose that we could all contribute to what would be an endless list of reasons that we should not get along. But Jesus has called us to peace.