Might just be me but my dupes are prioritizing other lower level tasks (1, 2, 3) over level 4 tasks. It's basic digging that's accessible and they're choosing any lower or higher level dig over a level 4. Proximity priority is turned off. Save/reload doesn't fix it. New world doesn't fix it. Also tried multiple times with different tasks and they just simply ignore level 4 tasks until every other task is complete
Set dupes to complete multiple different low-level tasks (1, 2, 3), as well as some different level 4 tasks. Watch dupes complete low-level tasks before level 4 tasks.