Hmmmm. It could be the re-used klingon bird of prey explosion? Sounds like there is something fishy no new special effects either. I don’t have the final frontier to check.
You’re thinking of the Bird of Prey explosion in The Undiscovered Country that was shamelessly recycled in Generations.
ILM was busy on Last Crusade and Ghostbusters 2, so most of the effects in The Final Frontier were done by a smaller company with mixed results.
The only thing I think I can spot so far from screenshots is the shot of the Enterprise A in spacedock from The Voyage Home was recomposited for TFF and the Excelsior in the foreground is gone.