Return the jacket under warranty. This is a common problem with RMC jackets so this won't come as a surprise to S&S.
I have said it at least twice before. Apologies for that, but it appear that this point triggers all my bad emotions:
Selling an expensive leather jacket with a hide that will outlast the wearer and combining it with a zipper that is BOUND to fail sooner or later (sooner in many cases...), makes absolutely no sense.
"Historically accurate" is a cheap excuse, in my book, as the hides uses are not "historical" either. Just use a working repro, for crying out loud!
In a way I am more frustrated with Aero than with RMC or Freewheelers. The later offer "take it or leave it" jackets, while Aero lets you customize your jackets with hundreds of lininngs and dozens of zippers. But won´t let you size up on them.
With the intro of Universal zips, this point is now relative, but a heavy batch of CXL FQHH still puts a lot of strain on a No. 5 zipper and Aero by default buries the zipper-tape so deep into the leather that the strain is even more enhanced (plus certain designs like the Highwayman with the thick leather fold at the waist stress the zipper even more by their pure design).
Lewis Leather, Schott, Vanson, Y2, Thedi - they all use larger zips by default. Nothing wrong visually, and I just feel more confident grabbing them. Not joke to fiddle with a tiny zipper in the pouring rain...
End of rant!