Consider retiring the effectively obsolete 10-year-old router you're using today, and moving to an AX-class router instead. Considering the age, and limitations, already being faced with your current router on the latest RMerlin firmware, I don't see how this model won't be going into EOL status very soon. Even if you don't run RMerlin firmware and just stock Asus.
The RT-AX68U, the RT-AX86U, and the GT-AX6000 will outperform your current router, even without AiMesh being needed.
See the performance improvement I would expect from a new, entry-level, AX-class router in your environment. And this is from (at the time) the best AC-class router available (RT-AC86U), which is already a huge jump from the RT-AC68U you have (particularly if it's the original version).
There are some odd regressions being discussed on the dnsmasq-discuss list from the PiHole guy (Dominik). https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2021q3/015598.html https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2021q3/015596.html I see Merlin is testing 2.86 out...
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