WARNING is no good reason for stopping a flow, but it's a heads up if any other issue happens later.
CRITICAL should be the most alarming log you're ever going to receive, it should be a good excuse to wake you up at 3 am to resolve.
A. Knote, S. Edenhofer, and S. von Mammen. 2016 IEEE Virtual Reality Workshop on K-12 Embodied Learning through Virtual Augmented Reality (KELVAR), page 5-10. (March 2016)