Systems not working

[revitworkbench]

hello, today for some reason, my duct system are not carrying from my duct to my fittings. This is very strange since ive never seen it happen before. For example I tried to use the "Cap Ends" button on some ducts and instead of inheriting the same system of the duct they are attaching to, they come in as "Undefined" and therefore show up as gray in my attached picture, shown next to a propertly system assigned endcap that might as well have been from yesterday (in pink). I first noticed this problem today when I was copying groups of ductwork around, by the copy in place, then move method. But the entire system was changed to "Undefined" inside the newly copy groups. Which is strange because Ive never seen that before either, and I do it all the time. But I chauked it up to groups just being groups (ie: weird and difficult) but when it started happening to all of my systems, in groups or not I am starting to worry.  Does anyone have any ideas what the heck is going on?

[Anonymous]

Well it seams that this bug has reared their ugly heads again.

it seems that once a duct system gets changed to supply the duct cannot be changed back to something else.  

here is what we are seeing as you can tell in this case there are no other choice to change the system to.

but here is another sample of an exhaust system.

so

has anyone figured out how we can fix this???

[RobDraw]

If a system is connected to a connector in a family that has a system assigned to it. You cannot change the system. Not a bug.

[nirmal_parikh3VUV7]

@luke.johnson The full details link you posted is no longer visible. I am having a similar problem for my BIM360 project on Revit 2021. I'm afraid purging the groups will delete all my groups that I am currently using for the project to show on construction documents.

[RobDraw]

You can't purge groups that are being used. Also, they all need to be ungrouped before they can be deleted from the project browser.

[luke.johnson]

For future reference, the live version of the solution post is at How To Fix A Revit Model When Duct and Pipe Fittings are Always Created Undefined » What Revit Wants...