Connection Pool ASIO connects indications of success with indications of use, which causes the underlying connection pool to assume a connection is fresher than it may actually be (we said we did IO, but actually we just haven't caused an error).

Because the connection pool it self checks connections out, marks them ok and then checks them back in to trigger a refresh, this causes connections to always seem fresh, never be heartbeated and never check against minConnections for dropping. This will likely cause connections to stabilize at some high water mark, rather than dropping down to minConnections.