Visible crew/equipment: During the landstrider sequence, before they reach the Crystal castle, you can just make out in one shot, the safety wire attached to the performer as he runs. (DVD extras says the landstrider performers had these wires all the time but this is the only time you see them).
Other mistake: The shape of the crystal shard is all wrong. In a flashback scene a urSkek is seen "shattering" the original, pure crystal by hitting it with a rod on one of the crystal's flat surfaces. For argument's sake we will say that in their universe it would be possible for this to create a spear-shaped hole in the crystal. However, the top of the shard is a rounded surface; it should have a flat, slanted top to match the top of the hole it came out of. Could pieces have broken off the top of the shard to give it the rounded shape? If that were true the final solution would not have worked; only the whole, pure crystal would restore the urSkeks.BocaDavie
Visible crew/equipment: Shortly after the scene in which Jen sees someone shatter the Dark Crystal in a vision from the Crystal Shard, there is a panning shot following Jen through the forest during which you can see the shadow of the camera in the foreground.