Are There Scenarios Where the Checks-Effects-Interactions Pattern Is Insufficient?

Yes, the Checks-Effects-Interactions pattern can be insufficient in cases of cross-function reentrancy. If two different functions share the same state and one of them allows an external call before updating that state, an attacker can exploit the first function to manipulate the state used by the second.

Additionally, in complex systems with multiple interacting contracts, this pattern alone might not be enough to prevent all reentrancy-related vulnerabilities. A holistic security approach, including reentrancy guards and thorough audits, is often necessary.