If they view it from the app it may not log. And if they just DL the coords and upload a find from GSAK or go straight to the logging page (i.e., the loophole for family members on premium caches) they won't show in the audit log as they did not visit the main cache page.
All three of my caches in Challenger Park have been muggled twice and one of them three times in the last few months. Best I can tell, no other caches in the park have been bothered. In the screen capture below you can see that all caches are active except mine. One of mine that is disabled isn't grayed out?? But, I looked at the others and saw none have gone missing in the last several months. So, I decided to look at the "Audit Log" to see who had been to the cache pages since the last find 'til it went missing. I don't see anyone who went and didn't find or log a find or DNF. But, I see they have been found by people not in the Audit Log. According to GC's definition the Audit Log is supposed to show everyone "who viewed your cache"
So, how could people be finding it yet never visiting the cache page?
I was trying to solve a puzzle cache that involved putting a zip code in the GC search box to get coordinates to project off of, but the new search function gives results in a new format that doesn't include the coordinates at the top of the page. After some looking around, I found if you use the "Advanced Search" link on your dashboard (the old one, not the new one) it gives results in the old format.