as salam alaikum
there is no certainity that single narrations (khabar al-wahid) from al-Kafi, with no external evidence to claim their origin (maqtu'iyyah al-sudur), are in fact from the Imams. Rather what Usuli scholars have said is that we can act according to its authentic narrations (al-sahih minhu), when proofs for it have been established.
There are several criterions to establish what has been said by the Imams but we consider no book of hadith 100% sound under all aspects and all narrations should be subject to rigid scrutiny.
With prayers for your success.