If you upgraded from an older version, and the /ipv6 nd have settings that in 7.23 trigger the sending of RA even if no /ipv6 nd prefix entry for the interface is present (for example DNS setting other than no, or MTU setting, I've not tested, but probably when the managed and other configuration checkboxes are active too), then 7.24rc3 will not do that anymore (will not send RA like crazy anymore). The entries will, for now, behave like under <= 7.22.
But if you open an entry, and make some edit, and save change, then RouterOS 7.24rc3 will assume that you've made the necessary adjustment, and will remove the warning from that, and will go back to the behavior introduced by 7.23 for that entry.
This is MikroTik way of mitigating the problem from this upgrade path:
Older version have "Advertised DNS" checked as default value on the default all entry -> Upgrade to 7.21 setting is migrated to advertise-dns=yes but it's no longer a default value, so it appears in export -> Upgrade to 7.23 and RouterOS send RA if advertise-dns is not no, regardless of everything else -> RA are sent on all interfaces.
With the hack in 7.24rc3 it becomes:
Older version have "Advertised DNS" checked as default value on the default all entry -> Upgrade to 7.21 setting is migrated to advertise-dns=yes but it's no longer a default value, so it appears in export -> Upgrade to 7.24rc3 and RouterOS does not send RA if there is no /ipv6 nd prefix entry for the interface, even if the entry has advertise-dns=yes -> RA not sent on all interfaces even if the interface=all entry also have advertise-dns=yes
but if you edit the entry, then the 7.23 behavior resumes.