Reduced increments happen when something, somewhere in the galaxy, is happening.
You might have a fire control set to open fire.
There might be an NPR vessel skirting the edge of sensor range (either yours or another NPR).
There might be NPRs fighting each other.
There might be an NPR vessel having fuel issues.
...
If the issue is "invisible," it's probably an NPR vs NPR thing. If it's endless, it might be two NPRs chasing each other back and forth through a stabilized jump point.
The solution is to figure out what is happening and rectify it, usually by making the vessel with the problem "go away." Scouting can help with this. So can opening the database using a sqlite browser and looking at the FCT_GameLog table.