@nads180 and @karuminu396 , was this a chair that you have used before and it suddenly stopped working, or is it a new chair you just placed? Some of the placement and routing issues can effect this for some reason.
Also, if this was a chair that you have used before in that same location, when did you first notice it not working? 🤔 I checked the Bug Report List and it wasn't listed on there, so if it is a bug it would probably be a new one, as we did have a game patch a week ago.
Finally, since you said they can both sit and rock in the chair, have you tried to sit in the chair and then direct your Sim to start knitting from a seated position?🤔 I tried this and even when they said their route to the chair was blocked, once they just sat in the chair they could start knitting if I directed them to do so. 🙂