This issue has been reported to the Symantec Development team. A fix has been released with ITMS 7.6 HF4 (DOC8949).
There is a pointfix available for SMP 7.5 SP1 HF5. Please see attached file "Pointfix_eTrack3791270_SMA_7_5_SP1_HF5.zip"
Installed SMP 7.5 SP1 HF5
HOW TO INSTALL THIS POINTFIX:
Workaround for previous versions:
It only happens when the "Use Application credentials" box is checked for that rule.
If the app ID is manually specified rather than using the App IP checkbox it succeeds and shows the available OUs in the picker for that domain.