"ME TOO!"
If the sim gets interrupted or stops the project and then goes back to resume the unfinished project later, they have the routing issue thought bubble and reaction like something is blocking them from getting to the usually usable (un-slotted) chair. When I have them sit down in the usable chair and resume an unfinished project either by clicking the basket in the inventory or clicking the chair, the sim still has the unroutable thought bubble and reaction.
The only work around(s) that I can find that seems to work 100% is if I have them start a new project by either clicking the basket or clicking the chair, then cancel that newer project and resume the old project. Then everything works as expected and the sim will resume all the projects once I ask and queue them up. It also works if I have them start a new project either from clicking the basket in inventory or clicking the un-slotted chair, finish the new project have them continue the old project once they are done with the new one.
I agree this happened after the most recent pack. When I first purchased the pack I did not see this bug. I have all packs except some stuff packs and the most recent game pack (I have all except: Luxury, Cool Kitchen, Kids Room, Toddler, My First Pet SPs and Journey to Battu GP).