That sounds like this bug? Did they stop bringing things to stockpiles as well, only cutting trees/crops/stones (basically responding to the harvest commands you give them)?
I too have got thread and cloth made. In my first play, the cloth was used to make a comfy bed. Have not gotten beyond that so far. This may be a silly question, but did you get the workers to harvest the plants? The weaver doesn’t take the fiber directly from the plants, in case that’s what you were expecting.