For some reason, when I tell a fleet to jump to a point several jumps away, some subset of the fleet will often take a different route from the rest of it to get there. Which means that if I'm not watching for this I may have my fleet arrive to attack, and then discover all of my heavy cruisers are still two jumps away (as a note, I first noticed this in kodiak heavy cruisers in 2b, but the Advent game I'm doing now has the same error but with the ships going the wrong way being more random)