QtStage and QtUnStage are subject to data corruption via a race condition if two events arrive in quick succession before the full operation can be completed. This is a critical vulnerability, as the result of two requests being processed by the singleton class at the same time is undefined behavior.

This can be solved either by removing the singleton decorator of the class or by moving class variables inside the relevant functions. The former is less predictable, as the reason for the class being a singleton is not well understood, and the latter solution is easy to implement.