side issue 
noun
A point or topic connected to or raised by some other issue, but not as important, especially one that distracts attention from that which is important: his foreign policy tended to be dominated by side issues...
- Although I will not discuss my personal beliefs on that point, I think it is important to note that any issue other than this, raised by either side, is a side issue with no real bearing on the subject.
- But that is a side issue to the questions I was trying to raise and get feedback on.
- A side issue here concerns the connection between these distinctions and moral realism.