Looking for general advice, as I'm not completely sure what is causing this behavior which I did not encounter until recently. I'm finding it quite annoying because it can delete imports if I comment out a line during development.
Adding the following to your settings.json file (you can access it on Windows with ctrl+shift+p followed by a search for settings)
"editor.codeActionsOnSave": {
... [other settings] ...
"source.organizeImports": false
}
Note: ensure that "editor.codeActionsOnSave" is not defined elsewhere (aside from language specific places), as this prevented the fix from working the first time I tried it.