Hi @lazyemu, sorry to hear about your issues. We have been unable to reproduce the issue unfortunately but it might be worth having a look at your environmental setup. For example, try to ensure there are no sources of infrared light such as open window or spotlight near the eye tracker.
IF you have programming experience, you could try to see if the presence variable is similarly affected on another sdk such as Core SDK or Interaction Library API.
Unfortuntely, as the Unity for Desktop API is no longer actively developed, there is little we can provide to resolve the issue from a SW point of view.