I'm not sure why this happens, but I have seen it occur sporadically on Windows builds in AppVeyor. I have been unable to reproduce it yet. Perhaps the condition is only encountered under load or with limited resources. Or maybe it's specific to PHP on Windows.
However, when attempting to execute getChanges() in the DirSync class the encoder will sometimes return an IncompleteType as the ASN.1 PDU. I'm not sure exactly how this would ever happen, or why it would be sporadic. If anyone else is able to reproduce that it would be helpful to get more details. So leaving this here for now.