A distinctive problem in upsetting papers by religious sceptic (10)
I believe the answer is:
diagnostic
'a distinctive' is the definition.
(thesaurus)
'upsetting papers by religious sceptic' is the wordplay.
'upsetting' is a reversal indicator.
'papers' becomes 'ID' (identification papers).
'by' means one lot of letters go next to another.
'religious sceptic' becomes 'agnostic' (I've seen this before).
'id' written backwards gives 'di'.
'di'+'agnostic'='DIAGNOSTIC'
'problem in' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for diagnostic that I've seen before include "Indicating the nature of an illness" , "Analytical" , "Computer program" , "Distinctive symptom or characteristic (of a disease)" .)