Tasks marking themselves "complete"

I’ve noticed many times that when I go to my open task page, one or two random tasks will show the green check box in complete as I land on the page, even though I have not clicked on it. I have to remember to uncheck it or risk losing it. I think this may be a bug in the system. It’s been going on since at least the summer but I kept forgetting to report it. Has anyone else noticed it? I fear losing out on a critical to-do reminder for one of my opportunities. Thanks!