What is the reason behind this strange censorship of a specific scene in Tokyo Ghoul?
The whole show was highly censored, as shown in this comparison album (Obviously spoilers):
https://imgur.com/a/tvt2r

The main reason is Japanese censorship laws, which are very different from laws in the West, but some people have mentioned that S2 was airing at the same time as some ISIS attacks took place, thus this might have something to do with TV networks censoring knives.