Not sure if this happens anywhere else, but in the seasonal battle against the Consumed Holiday Snowcat, my pack will suceed the encounter but the text will say they failed instead. See:
Image 1: screenshot of the battle with my team clearly healthy and the enemies being almost defeated. Note the festival widget at the top that remarks that 2 Icerun bosses have been defeated.
Image 2: the result of that same encounter, not even a minute later. It reads as if my pack has lost the battle, though the event widget above has registered the victory and says I have defeated 3 bosses now.
This has happened every time I won against the Consumed Snowcat, although I couldn't get evidence as I didn't expect the error.