In general, we see a pretty consistent trend of Starfleet incompetence post-TUC, starting chronologically with the fact that Starfleet was completely ignorant of the Nexus passing by Earth until the Enterprise-B received a distress call from ships trapped in it.
To be fair, no one in Starfleet even knew what the Nexus was until Guinan finally told Picard in Generations.
At the time of the Enterprise
-B, it was believed to be a powerful energy/gravimetric distortion--one of many space anomalies (a.k.a. weird stuff) that pop up randomly across the Galaxy from time to time.