When a UCP-enabled data source is initialized (and a connection obtained), it registers its UCP pool in the Universal Connection Pool Manager. However, if you use a :reload operation and try to use the same data source again, the first attempt to obtain a connection will fail, because the old pool is still registered under the same name (the name is denoted by the ConnectionPoolName property of the data source). It looks like it automatically de-registers after the unsuccessful attempt, so the second attempt will work.