Illustrator 3D object revolve artifact

Hi there.
I made this colourful 3D drop for a print service in Illustrator, (powerful 27 iMac, latest updates), with 3D revolve and map with multi colour gradient for mapping.
The drop is just 3 nodes but sometimes it's split in two.
I've re-done this 3d design many times with different gradients and changed the nodes but always this line.
When i enlarge the line may disappear for certain magnifications but the reappears.
I'm happy to send the file for evaluation.
All I can think of is that it breaks the code for whatever reason.
I'm new at 3D with design but I have extensive 2D design and decades of Photoshop and Illustrator experience.
Any ideas?