Complex sentence: It can take surprisingly long to revert vandalism even on the TFA, which is the most viewed page on any given day; it is not uncommon for TFA vandalism to remain for several minutes before being reverted, by which point many people have already seen it.
Split into simpler sentences: It can take surprisingly long to revert vandalism even on the TFA, which is the "most viewed page" on any given day. It is not uncommon for TFA vandalism to remain for several minutes before being reverted, by which point many people have already seen it.