Using both Endnote Web and Desktop

Hi there I have four questions

1- my endnote desktop recently started to hang every minute I used it, I have deleted it and MS word (MAC) and reinstall both but the same issue keep happing (any suggestion)

2-The I decide to go for endnot we but still another issue

I have sync my endnote desktop library with endnot web.

 Whihle using endnot web and I open any old file where the references was inserted for desktop and I try to ‘Edit library reference’ I get this messages  ‘The reference no longer exists in your library.’ (on the web)

3- Whihle using endnot web when I edited any reference in endnote web and try to ‘update citations and bibliography’ I could not see the changes in my document

lastly, I have made my own referencing style how can I upload it to be used in my endnot web