I found this quote from an anti-Islamic website :
"The opinion of the majority is that these readings are Mutawatir. However, one opinion is that they are Mashhur28 …. The truth in this regard is that they are Mutawatir from these seven [Qurr’a]. As far as their Tawatur from the Prophet (sws) is concerned, this is debatable. For the chain of narrators of these seven are found in the books of Qira‘at. These chains are transmission from a single person to another and do not fulfil the condition of Tawatur neither from the first narrator to the last nor in between. (Zarkashi, Burhan, 2nd ed., vol. 1, [Beirut: Daru’l-Fikr, 1980] p. 319)"
Can someone shed some light on this matter? Did some Imams including Zarkashi had reservations on the textual veracity of the Qur'an?