Yeah, if the manager isn’t giving you a specific plan and goals to improve performance then you should move on.
It’s hard to know for sure but I would interpret what you describe as the manager building a case for dismissal with cause. Since the company can let you go without cause at any time they are doing this either to save on unemployment benefits or as a precaution against a lawsuit. The manager is not telling you anything because he’s made the decision and now just has to avoid HR legal troubles.
Regardless of the reasons or corporate maneuvering you should focus your efforts on moving on. If you can’t make your current situation better then any time and worry you give to it is wasted. It’s easier to get another job while you’re employed so take advantage of the apparently slow process at your current job.
