Reasons for failing (Garda) clearance?

Hi, I’m currently at the Garda clearance stage for a civil service role, I presume it will take quite some time for me to hear back given the waiting times I’ve seen on this subreddit.

I have another job offer in the private sector which has given my an imminent deadline to inform them whether I’m accepting it or not. While I want to decline it (prefer the public sector role), I don’t like the idea of declining a set-in-stone job offer for a role I haven’t been given a formal offer for yet (as civil service don’t give you the offer until you’ve passed Garda clearance).

Hence, unless I’ve committed some crime I’m not aware of yet, I’m wondering if there are any plausible reasons I may fail the Garda clearance stage and not get a subsequent offer from publicjobs?