check on your daily view with hourly time. All items should have the blue bar next to it to show up on the monthly. If no blue bar then you are setting the status as free and they do not show up on monthly. Otherwise do a soft reset and hopefully it'll show up again.
Just in case that doesn't work, click Tools, then Categories. If any categories have a check, only those categories will show a blue reminder. Clear all checks and all categories will show.