Greetings and Welcome
We had the same problem in the bath.
Our dust wasn't attached.
Pull the grill off, remove the screws, reach in and grab the duct, reattach and put it back together.
I put a hose clamp like the ones that come with the sewer hose so it won't happen again.
We had very little flow from the couch vent, duct was attached. Better flow after I removed 15' of extra hose.