Install Issue? Files Gone

No, it just appears like the server might be linked to a different account.
Edit: Syno will usually block you from installing a version that’s not made for that particular platform (e.g. installing an ARM package on an Intel NAS).

Can you run the following URL with the same IP → http://[Syno IP]:32400/identity
This should show you an unformatted piece of XML – does it show claimed="1" or "claimed="0"?

You could give this guide a try…