Hi ! I am a 3a user and never encountered or seen such a bug. This is very strange, make sure to report it in Settings >Tips and Feedback> Feedback. But honestly, if it is as bad as you described it, this may be a hardware issue. Consider contacting Nothing Support in this case. My 3a is extremely fluid and has no lag at all, never seen any app crash since I bought it.
Hope this will be fixed for you soon !