Hi. The behavior you describe is expected.
Having two separate named users making changes to the same survey is not supported. This technical limitation is rooted in how items are managed in ArcGIS.
When you first copied the project, the survey folder carried over the iteminfo file which indicates who is the owner of the survey. Once signed-in Connect will hide all surveys you do not own to prevent you from overwriting surveys from others.
After removing the iteminfo file, you temporarily tricked Connect, but when Connect attempts to make updates on the Form and Feature service items it fails, because ArcGIS does not allow edits in these items unless you own them.
There is really no way, to my knowledge, for two different accounts to effectively collaborate with updates to the same survey.