In The Last Jedi some key new technology is assumed to be the reason why:
The First Order can now track ships through hyperspace without the use of a tracking beacon.
Not long after this, several characters come up with a plan for how to disable this tech. As part of their discussion holographic schematics showing both the appearance and location of this tech are shown.
If this tech was new how did the Resistance have access to the schematics showing both what it looked like and where it was physically located?