The priority system for the Harvest ability is not working at all. If I set a "priority 6 dig" (or any other activity, such as building tiles) and a "priority 9 harvest", the Duplicants will always do the harvesting last. This is REALLY annoying, because you want to harvest ASAP, to allow the plant to continue its growth cycle. So if I have lots of jobs queued (dig, build, etc) and a plant becomes ready for harvest, I have to cancel all pending work in order to get them to go harvest the plant, then make them sweep it up and put it in the refrigerator, then redo all my former build commands.
Also annoying (not really a bug) is that when you give the command to Harvest, the Duplicant leaves the food on the ground. This forces the player to babysit harvesting in order to command the Duplicant(s) to sweep up the food and put it in the fridge. This is also a huge time waster, since a Duplicant has to walk to the plant to harvest it, then a second Duplicant has to walk there to sweep it up (or in my current case, climb 3 or more stories of ladders). There should be a gameplay menu option (selectable radio button) for "automatically sweep up food when harvesting".
As for the original point of this post, food and oxygen are the two most important things for Duplicant survival. A priority command to harvest food should take precedence over just about all other commands. I don't believe you have this in-game at the moment, but the Priority System needs to have a built-in "second tier" to it. In other words, if a player has these 4 things all at the SAME priority level - dig, build, harvest, sweep - there should be an "order of precedence" such as harvest > build > dig > sweep.
With your Duplicants all busy with any other work (ex: Set them a ton of level 6 priority digs), when a plant is ready to harvest, select the harvest option and select priority 9, then click the plant. The Dupes will not stop digging.