Hello- I am working on a project and having some failures- this started as a 3d scan and working on modifications-

I have used some of the surfaces to make half of the model (as the scan was not symmetric) and attempted to mirror- I get the following error   one or more features in the mirror feature are no longer in the model  I have not run into this issue before - any thoughts?

I proceeded to split some surfaces and deleted some faces in attempt to "filled surface" and cannot a good result- maybe there is a better way?

you can see what i am trying to achieve