1- Sunnis have many narrations in Bukhari and other words that claim Tahreef happened in the Qur’an. Please don’t let these people fool you. If their issue is with Shias and tahrif, their books have more hadiths about tahrif. See the following:
AI-Bukhari in his Ta'rikh records Hudhayfah as having said: "I had learnt the reading of the Surat al-Ahzab from the Prophet (S), but I forgot seventy of its verses, which I could not find (anywhere).”110 Also, Abu Ubayd, in al-Fadd'il, as well as 1bn al Anbari and Ibn Mardawayh, report `A'ishah as having said:
كانت سورة الاحزاب تقرا في زمان رسول الله(ص) مائتي اية فلما كتب عثمان المصاحف لم يقدر منها الا على ما هو الان.
The Surat al-'Ahzab as read during the Prophet's days contained two hundred verses. But when 'Uthman wrote the mushaf, he could not find more of it than what it is now
In this narration, it is claimed Sura Ahzab was much longer!
Also see this hadith by Aisha:
Reported ‘Aisha (RA): The verse of stoning and of suckling an adult ten times was revealed, and they were (written) on a paper and kept under my pillow. When the Messenger of Allah (pbuh) expired and we were occupied by his death, a goat entered and ate away the paper. (Sunan Ibn Majah, Hadith 1944)
See this hadith in Sahih Muslim about the “verse of stoning being omitted from the Qur’an”:
Abdullah b. ‘Abbas reported that ‘Umar b. Khattab sat on the pulpit of Allah’s Messenger (may peace be upon him) and said: Verily Allah sent Muhammad (may peace be upon him) with truth and He sent down the Book upon him, and the verse of stoning was included in what was sent down to him. We recited it, retained it in our memory and understood it. Allah’s Messenger (may peace be upon him) awarded the punishment of stoning to death (to the married adulterer and adulteress) and, after him, we also awarded the punishment of stoning, I am afraid that with the lapse of time, the people (may forget it) and may say: We do not find the punishment of stoning in the Book of Allah, and thus go astray by abandoning this duty prescribed by Allah. Stoning is a duty laid down in Allah’s Book for married men and women who commit adultery when proof is established, or it there is pregnancy, or a confession. (Saheeh Muslim Book 017, Number 4194:
Now you can come back and say: oh, this hadith has a “different” interpretation…it means x, y, z. Or the chain of this hadith has a “weak” narrator!
Ok, we can do the same. Those alleged hadiths that claim some parts of the Qur’an went missing are either weak hadiths or they have a different interpretation. The fact that these Sunni friends of yours only mentioned the “Shia Tahrif” hadiths and never mentioned to you what it’s in Sunni hadiths should tell you a lot about their “honesty.”