Currently, a snapshot is taken live, without shutting down an addon.
In some cases, this will lead to a corrupted copy.
I experience this with the MariaDB addon. There is an open issue about this specific add-on, however, I imagine there are more add-ons that require a shutdown before a backup can be made.
Although this sounds like a feature request. This was a WTH moment for me because some addons are broken by design now.