On July 28th, I received both email and Android app notifications that three tasks were due (all are set to repeat monthly on the 28th). In the web interface the notifications are still visible, so I've attached a screenshot to show they were generated on the 28th.
Last night (the 29th), I finished the three tasks and went to check them off, but they were no longer in my task list (either web or Android). I went to my "Completed" list, and they aren't there either. The tasks do show up on the 28th of August (when they should next be due). These tasks are private to me, so no one else could have marked them finished.
Please attach any supporting materials, such as screenshots.