Reckoning got changed in classic as a side effect of fixing a bug with Hand of Justice and got broken (and apparently sword specialization for warriors got broken with the same HoJ fix). They fixed those things, but reckoning as a result of all of these changes does not act anything like it did in vanilla. In fact, if a paladin with reckoning gets crit multiple times in quick succession, they don’t even auto-attack. It does something funky with the attack timer.
For instance, here is a blue post about fixes to reckoning: Reckoning after yesterday's patch - #123 by Aggrend-1483