Modern world? Check.
Existence of a society that navigates through things and events that are supernatural?
Check.
A seemingly normal main character who somehow manages to find herself in the middle of all that action, transforming her life into that of a supernatural agent of sorts?
That’s a check. Yep, something definitely seemed similar to me when i saw it in webtoon a couple of minutes ago. It’s a new one i think, but i might be wrong.
Edit: I love that pumpkin headed agent.
Looks like the artist has been doing stuff on it for a while (early 2016), but has recently moved to Webtoon so only has 3 issues up dated 20 September. Pumpkin guy definitely looks like he is rocking Chaos 
More like ‘every single clichè of contemporary urban fantasy? check’. Vague, paper thin analogies, and honestly Third Shift Society isn’t even that good.
From the description, it sounds similar to popular Webtoons like The Uncanny Counter, Sweet Home, or Ghost Teller, but without knowing the exact art style or title, it’s hard to pinpoint which one they saw. If it’s a new one, checking Webtoon’s recent releases on 블랙툰.store under the supernatural or action category might help.