After doing a Defera Invasion event last night, I've been stuck with 17 of the unstable matrixes in my inventory. You're suppose to use them to blow up borg devices located all over the map, but they do not disappear when the event is over. They cannot be destroyed and they cannot be sold. I tried to drag it to my replicator and all it did was switch it out with the remodulation device I had slotted into my character's first device slot.
The only way to get rid of them (that I've found) is to take the mission again and use the ones in your inventory. Don't take the offered ones of course, that will make things worse :p Drop the mission after you've used them up.