A "significant loophole" is a flaw or gap in a system or law that allows for something unintended or undesirable to happen. It is an important or noteworthy weakness that can be exploited or taken advantage of. Full definition
I realized, sitting there on his couch, that there was a pretty significant loophole in Tommy's payment plan: What if we never completed production? (vulture.com)
Loan insurance is expensive and often contains significant loopholes that protect the insurance company and not you. (freedomdebtrelief.com)
«In fact they've included a pretty significant loophole. (wxxinews.org)