7. Three Timelines, Three Beams, Three...Enterprises?
The climactic episode of The Next Generation, All Good Things, features a breakneck story of temporal hopping, paradox discovering and family building between the crew of the Enterprise-D. It is clearly a triumphant finale for one of the most popular iterations of Star Trek, serving as a stronger script than the first film, Generations.
However, while in the Devron System in the past, present, and future, Jean-Luc Picard initiates a scan from a topographic imaging scanner, primarily designed to scan the anomaly that's appeared. Once the event horizon has been breached, it is discovered that the union of all three beams is what is in fact causing the anomaly to begin with. They have the exact same resonance frequency, as though all three were coming from the Enterprise-D.
In two of the time periods, this is accurate. In the past and the present, Picard is aboard the Enterprise. However, in the future, Picard is aboard the USS Pasteur, an Olympic-class ship that is most decidedly not the Enterprise-D. While that ship does eventually show up, it is not the origin point of the beam.
Reportedly, writer Ronald D. Moore noticed this, but left it in any way, as changing the error would have been too costly to be feasible.