Issues with the widgets administration screen are usually an indication of Javascript problems (perhaps due to plugins interference). Parabola does not use the customize screen so I assume you are referring to its settings page (under Appearance > Parabola Settings). This can also be affected by Javascript issues caused by malfunctioning plugins.
Since the problem appeared after a WordPress update, the most likely cause is a plugin that’s no longer compatible with the current release. I recommend temporarily disabling all active plugins to check if the issues disappear, then reactivating them one-by-one to identify which one is the culprit.