Thanks for letting us know the bug fixes seem to be working!
I'm sure the experts aren't completely infallible That said, for the calibration movies, multiple experts examine each movie, and then when there is disagreement, it goes to committee and they discuss the movie until they reach a consensus. If there is not consensus, then the movie isn't used.
You observations are apt. One formal definition of a stall employed by the experts is the absence of apparent movement in the vessel. By this definition, a vessel that appears solid white, would be considered a stall. However, this presentation of a stall accounts for only about 5% of stalls. We are working on a more advanced tutorial that includes lots of examples and considers some of these more nuanced cases. So if you are now saying, "how could anyone possibly get those ones right if you don't tell us that a stall can look like that", then you are absolutely right! At this stage, we are not expecting folks to recognize that particular type of stall, and in those cases the expert answer will be confusing. Again, this will change soon
Regarding the case where you have observed stationary black gaps and the experts called it flowing, I can only speculate. Sometimes, more than one vessel appears within in outline - and in those cases, occasionally a stall occurs in the vessel that is not the "target" vessel, and can be a red herring. The target vessel is the one that most closely follows the shape of the green outline. However, because we realize that even experts can make mistakes I would like to tell you about a feature that we will be adding soon, which will be a checkbox that allows you to flag bad feedback on the feedback screen. If you check that flag, an expert will look at the vessel and comments to see if there is an issue, and either provide clarification in the expert comments or, if justified, change the expert answer.
We are glad you find the game addictive and, just as a teaser, I will let you know that we have some new features planned to make it even more so. So please stay tuned - we are just getting started!
Thanks again for this useful feedback. Perhaps one of our annotation experts will also chime in.
All the best,