It appears a bug is introduced in 2.0.4+ when MinPoolSize and MaxPoolSize are set via SocketPoolOptions (MemcachedClientOptions.cs) and MinPoolSize property in SocketPoolConfiguration.cs has a check to ensure it's less than MaxPoolSize. The issue is when both properties are set in SocketPoolOptions, it will throw ArgumentOutOfRangeException since the default values are 10 and 20 respectively and when I set 50 and 500, it will check MinPoolSize (50) against MaxPoolSize (20). It does not know about the new value yet.
Here's the example that will trigger the exception.
var c = new SocketPoolOptions { MinPoolSize = 50, MaxPoolSize = 500 };
var options = Options.Create(new MemcachedClientOptions { SocketPool = c });
var config = new MemcachedClientConfiguration(_loggerFactory, options);