I had Tasks open (in Microsoft Edge on Windows 10) and was working in another Edge window. When I returned to Tasks, some tasks from my main non recurring task list were missing. I'm not sure how many were missing, somewhere between 2 and 20(?), because I cant remember what all of the tasks were. I'm left with 19 tasks, so it wasn't an enormous task list. Obviously this is hugely frustrating and disappointing and I'm now reluctant to trust this otherwise very good app again.