I started 2 boss fights 1 co op and 1 single and those are the only bosses I have open and it says 3 but I only have 2 open though. I've also not played the game for 6 days not sure if that helps.
you were possibly in the middle of a boss fight and time ran out(ive noticed after beating the boss the count drops to 0) also zombie slayer crashed recently so the counts might be funky
