The router itself plays a part if there are devices directly connected to it (i.e. via ethernet or wifi, connecting to the router hardware directly with no intermediate devices).
That's why I mentioned bouncing your entire network, too (switches, APs), which will bounce the client interface on all devices because ethernet and/or wifi will briefly go down.
You didn't say how many devices you have, nor if you are operating in a home environment or something else where the bouncing of the network is not an option (and office, school, retail location, etc.).
Yup... that is precisely why it doesn't work... the router isn't involved at all, except currently (or probably the recent past) insofar as issuing the DHCP option 6 pointer to the PiHole via the DHCP server.
But yes, in 12 hours or less, this should be a non-issue, provided that you have removed option 6 from the DHCP server.
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Thanks! 