I don't know if this also applies to later versions of the mod, 17.10 is the version I am using.

When a task is set to auto-consume the required items, it sometimes just eats the items without counting up.

For example, collect 8 diamonds. If I pick them up one by one or even 4 at once, they just vanish and that's it. The quest still says 0/8. If I get more than 8 at once, it works properly most of the time (every so often it takes the items without counting them, but it's rare when taking them all at once).

The quest I made was an auto-consume and auto-complete quest that checked if the player was in a specific dimension, then it consumed one of an item and gave one of a different item. Cooldown of 10 seconds. On average, nearly 50% of the items were lost.