Microsoft has just updated the following KB Article:
Task sequence fails in Configuration Manager if software updates require multiple restarts
Symptoms:
Assume that a Microsoft System Center Configuration Manager task sequence that uses the “Install Software Updates” step installs a software update that triggers multiple restarts after the task sequence successfully runs the Install Software Updates task. In this situation, the task sequence can fail and generate the following error message:
Task Sequence environment not found
Full details at:
https://support.microsoft.com/en-us/kb/2894518