If a user attempts to set a quest set name to the same as another quest set (regardless of casing or even if the conflicting set name is its own) the game soft locks.

The reason appears to be a mistake in the while loop on this line:
https://github.com/lorddusk/HQM/blob/1.12/src/main/java/hardcorequesting/quests/QuestSet.java#L313

Because found_conflict never resets itself to false at the start of each loop. The break statement will never be called after the first conflict even if the name has been resolved and the inc value stops incrementing.

PS: The characters "%s%d" do not specify their argument indexes which may or may not be an issue (I still need to test this)
Double checked and it works fine in this use case without specifying indexes.