Thanks again for sharing this data.
First, I have a question: where did this data come from? What product, and what format was used to import it to Fusion? Can you share the source neutral (STEP/IGES) file?
Second: I don't think that this is a Stitch problem, per se. I think that some of the data is bad - whether it was bad in the input data or became bad on import is not yet clear.
I tracked down the problems to 3 bodies. All are in the component "043745;2,NMS-RELEASE-00XXXX-000XXX" underneath "G - Endcap"


The first problem is this body:

As near as I can tell, this is an open surface body, there is no thickness to it. Stitch is not going to help you here. Thicken, however, will work. I don't know if there is some missing data, or what...

specify a thickness here and it will turn it into a solid.
The second problem body is this one (Body9):

this is a very strange body. The different colors here are showing that the surface normals are not consistent, within the same body. it's not clear whether this was in the input data or somehow Fusion has flipped them. I spent a long time trying to get the normals correct (using Unstitch and then Reverse Normal in the Patch workspace), but was unable to get it right. If we have the source data, perhaps we can figure out this issue.
The third problem is in this body (Body14):

Specifically this face:

The circular portion on the right hand side should be open and connected to the cylindrical faces from the hole below. I tried to fix this face, but have not yet been successful.
Sorry that I have not been able to resolve these problems for you. If we have the source data, we can maybe learn more.
Thanks for your patience.
Jeff
Jeff Strater
Engineering Director