Hi @LN and @danbjoseph ,
I just tried to resend a form from collect to Central, no new submission appears In Central.
Do I miss something ?
The context is a form sent by a colleague in May that does not appear in Central. Resend it does not change anything.
If it is the reason why this form doesn't appear I have to go deeper t understand the problem.
What happens when you try to resend? Does Collect show any kind of warning or error? Does it show that the submission was successful? If it is showing that the submission was successful, then it's likely that Central does have it already. How are you determining that it's not in Central? Could something in your processing and analysis pipeline be missing it instead?
I do not have any personal process before pulling submissions from Central 
The try I had on my phone correspond to that case.
I'll try with my colleague's phone as soon as possible to better describe and understand what happens.
Ok I think I understood the issue.
The form has been sent (visible in the instance folder) and edited after (in cache folder as an xml.save file).
What probably happened is that the user initiated a send and/or autosend ran and at that same time they made an edit. This is one of the many reasons that we've made finalization truly final in the latest Collect version.
If you want to be absolutely sure that you're not losing something, you could pull the instance from the device using adb or view it using a text editor to compare with what's on Central. Maybe the user did make a legitimate edit that you'd want to apply on Central.
I resent the whole form after I renamed the instance file and directory and I got all the data in central. 3 were duplicated and I deleted it from our final database.