Seems you might check your lockout strategy first. Seems to be quite easy to perform a DoS attack on your root users which an attacker might do first…
That said, you might exclude the “Default accounts” family and set the preferences in the NVT “Options for Brute Force NVTs” (OID: 1.3.6.1.4.1.25623.1.0.103697") like “Disable brute force checks” and “Disable default account checks” to “yes” to disable such account checks.
However, as I said, I strongly suggest to revise the lockout settings on your devices first…