As a starting point, if your issue is not performance related, take a look at trace logging below. If it is performance related, a good first step is to enable a little graph with Ctrl-C that shows two horizontal bars:
- A purple bar, representing physics, that should never be close to 100%. This bar indicates how much time is spent doing physics calculations (which are done on your CPU). If that bar behaves erratic and shoots up to 100%, go to the section on performance logging and try to capture the issue with that enabled.
- A green bar, representing graphics, that (unless you cap your framerate) should be close to 100%. This bar indicates how much time is spent rendering graphics (mostly done on your GPU). If the bar behaves erratic, or somehow your graphics don't appear to be smooth, go to graphics logging.