Basically, for one of my factions, the mineral packets that have been sent from some civilian mining colonies only extend half-way to their target, and instead of send more out, they're now just piling up on the colonies in question. They show as contacts on the system map, and there's a huge pile of them over the sending planets, and enough to extend half-way to the main planet but they just stop there.
What do you mean, they just stop there?
On the system map, a mineral packet contact should give info on its speed. At what speed are they traveling? As far as I know, civilian mining colonies (CMC) always sent their packets at 1000 km/s.
More importantly, what's the distance between the colony and the packet destination? Over 25b km? When the packet travel time is over, say, one year, you might want to use freighters instead of mass drivers. That or not buy the minerals, taking tax money instead. You can also abandon the colony and reestablish it, deleting the CMC completely.
The same problem arises with comets, when they travel very far outsystem, if you keep sending 1000 km/s mineral packets you can clog your game up with moving contacts. Mineral packets in transit are my personal #1 reason behind my games slowing down, so I'm extra careful about that now.