I run into the same issue as well. The Reminders window is not sized appropriately for all the reminders and the buttons to show up properly.
This is something that Microsoft needs to fix.
However, in the interim, I have found a couple of ways to fix:
- Restarting the computer and launching outlook seems to fix it temporarily... but then the issue reoccurs after a few hours or so.
- When the issue reoccurs, I use wininspector spy++ tool to look for the reminders window and add the WS_THICKFRAME style to the reminders dialog. That allows me to resize the window.
- Launch wininspector and select the window, use the right click and choose the "edit window styles" option.
- In the "edit window styles" dialog, double click on the WS_THICKFRAME from the right pane to ensure that it moves to the left pane. And close the dialogs.
- Notice that the dialog becomes resizable.
- And once you resize the window, the dialog remains that size till outlook is closed.