That is most commonly an input problem. How are you entering your grades – mouse-clicking on the button (or screen-tapping in the mobile apps), keyboard shortcut (or swipe/gesture in the mobile apps), remote, or something else?
If this is happening when you’ve recorded the correct grade, it sounds like a sync conflict – which can happen when you make changes (or allow add-ons to make changes for you) on multiple unsynced devices at the same time. That has the potential to leave cards in an inconsistent state.
See this thread for how to fix and prevent that: Scheduling differences between Anki desktop and Android - #4 by Danika_Dakika .