It happened also in different DSP, for example, it happened to me in Taboola, outbrain, Gemini .... when you contact the support they will like you to review the most case
but in my case, that was black camp so I cannot contact the support after a review that's like burning my camp so the things are that somedays it was spent and some days even not 5$ was spent usually its a bug or problem with the bidding that you not getting any Exposures... in my opinion, try to delete and republish your camp and if it's not fixed contact the support.