That seems fantastically inefficient indeed: other than going for a quadratic approach, why would you count how many times you found overlapping? Just return false, can't you?

Paste your code here using proper markdown and mark your post as having spoiler content if you want someone else to take a look at it.

I am struggling to see fault with my code as it completes quickly in the sample tests and extra testing. How can one tell if their code is inefficient?

Infinite loop or inefficient algorithm.