Amina Inloes, Amina Inloes is originally from the US and has a PhD in Islamic Studies from the University of Exeter on Shi'a hadith. She is the program leader for the MA Islamic Studies program at the... Answer updated 1 month ago

https://muflihun.com/muslim/8/3422

Anyway it is just a single hadith whereas the Quran has been transmitted in a lot of ways, so it is probably just an erroneous hadith and doesn't pose a serious challenge to the authenticity of the Qur'an.

Besides, if someone was going to intentionally lose a part of the Qur'an, one would think it would be about a more controversial subject than how many times a baby should be suckled to be mahram. And it is unlikely that it would be lost accidentally.