Regexes Misparsing
Design your regexes to be able to capture all possible variations of your data. By carefully creating and testing your regexes, you can make sure that Advanced Analytics doesn't miss data that would prevent it from being able to model a specific field.
Design your regexes to capture edge cases for how a value might appear in the log. In many cases, regexes are initially built to end when a space or an array/log-constructor-like character (':','[', '}') is used to end the regex. You will need to balance the requirements to allow a broadly tuned regex to capture what should be required, as well as limit how far the regex is allowed to capture. Sometimes a regex change is required due to a space being allowed in a filename, or the log management system happens to be appending forward or back slashes.