The bugtracker post in question: https://www.warmane.com/bugtracker/report/90261

Mind you, this isn't the only bugtracker post related to this bug (arcane missiles losing missiles), but this is the most recent and the "fixed" status of this is a blatant lie. I get frequent lag spikes of 1k+ (despite 1gig cable internet) and this seems directly related to the missing missiles. I honestly can't speak about if/how often this happened on retail or other realms because it was such an infrequent issue I chalked it up to myself clipping the channel. This I can 100% guarantee isn't happening now as I've added a [nochanneling] mod to my macro for arcane blast, in an attempt to remedy these missing missiles.