Looking under services-->ISC DHCPv6-->LAN the page looks like the attached photo. I assume there are many missing fields, any idea how to correct this?
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So I uploaded a recent backup and it seems to have fixed the issue. Not sure what caused it but it's back to normal now.
If this keeps happening in the future please check your storage device (HDD/SSD) with one of the tools provided in OPNsense :
- nvmecontrol (Available by default)
- smartctl (Plug-in you need to install)
And perhaps a file system check too!