My buddy pokemon (Feebas) has found candy but the last two haven't been added to the candy and it still sits at 97 but should be 99. Help?
The most likely answer is that you are seeing in-game notifications that your buddy found a candy, and these notifications can easily get out of sync with the actual game and repeat. I've seen notifications for raid eggs appearing or hatching multiple times and notifications for raids that are not even within distance of the nearby tracker.
Feebas should only find a candy after walking 5km, if you are ensuring that the distance is being recorded and are still not receiving a candy after walking that far then you have a significant issue in the form of a bug. Only Niantic would be able to help you with that.
In addition to Kadima's answer, buddy candy can only be accumulated up to a maximum of 40km in the last 24 hours. This is a dynamic window, not based on the calendar day, so if you walk 40km between 2pm and 10pm on Monday, you won't be able to start racking up any candy again until 2pm on Tuesday.
This won't give you a "Your buddy found a candy!" toast notification (so if you're seeing that then this answer isn't relevant), but it will reset the distance progress bar in the buddy page, so it will look like a candy was awarded even though it's silently failing due to the cap.