Mark,
I had look very closely to the photos.
Here is what I think what might happen.
How you mount and glue the servo? Where is the servo? Could it happen the servo plate came off during flight and take the half fin with it?

Usually the fin only can break off if you got flutter. Unlikely it will break for no reason. Even the spar are made from balsa.
The structure of the fin is seal balsa skin composite. That is strong enough.

I had test the model over the speed limit and pull until it break. The stabs and verticle fin stay in one piece when I pick the salvage.
Ehab plane pancake hard to the ground and tumble 200ft away. The stabs and verticle end up with some scracthed. No structure damage at all.

But I do got other two customer reported to me that they got flutter with they verticle fin.
After they landed and find the flutter cause by the servo stripping gear. The servo they using is not metal gear.
Stripping servo gear can cause by few things. Overdrive the servos, bump servo during transport and sloppy installation also cause flutter until the servo gear give up.

Mark,
If you return the fin back to Cermark. We can give you Ehab verticle fin no charge. If you have any problem return the fin.
Give me a call. I'll fix that.

The next shipment of new improve Viper Jet is coming late June.
I be flying to the factory few weeks before to do quality inspection before is final.

I do put alot time and investment to Viper Jet. Bad rumor do destroy my business.
So I only ask one big favor from everyone of you. Please take resposible for your post.

Goodnight,
Tam