What is the meaning of the narrators' repeated use of the phrase "akhbarana" (he informed us)?

We have not come across anyone who pointed out the existence of this repetition in the books of Hadith. Perhaps its cause is the omission by some narrators of their shaykh due to his fame, like the omission of Abu Bakr al-Qati'i from the isnad of a hadith in Imam Ahmad's Musnad in Ahmad Shakir's edition, where it became (حدثنا حدثنا - he narrated to us, he narrated to us) instead of (قال القطيعي حدثنا عبد الله حدثنا عبد الله بن عون - Al-Qati'i said, Abdullah narrated to us, Abdullah ibn Awn narrated to us). The repetition might also be an error from the scribes or printers.