When restarting a Z/OS job, the RestartPlus dialog box now *requires* the following parameter:
Return Code for RUN TIME MODULE
This was not required in V11.x.
This has been identified as a bug, and has been approved for the following release:
AWI 12.1.2 HF1, planned release July 5th, 2018.
Workaround: Manual re-submission of affected jobs, or utilize the Java UI.