I tried to replicate the issue but it works well. You possibly made a typo in here calling onFetchError(err))

useFetch('put', `factor/${props.apiRoute}/${factor.id}`, {}, factor, getFactorListData, ({err}) => onFetchError(err));

I made an working sample, you can check
https://stackblitz.com/edit/vitejs-vite-pnqmeoud?embed=1&file=src%2Fcomponents%2FStuff.vue