This kind of denial of service for autocompletion and the associated continuously increasing memory usage is unfortunately the current outcome of severe performance edge cases from type inference, which the New Type Solver is more prone to as we’re working through these issues. You can avoid the problem today by opting out of using the New Type Solver while we continue to work on these issues. In the interest of making our tickets manageable, I’m closing this as a duplicate of New Luau Type Solver - Type Solver Doesn't Activate.