I naively bought the Linksys WRT 1900AC about when it released because it claimed dd-wrt support at release.

Then the dd-wrt folks mentioned that Linksys never actually gave them hardware ... and if I recall, hadn't really been included in the plans to support it at all.

So then I waited and found whenever I looked for the dd-wrt firmware, it always had lots of caveats and known issues.

I gave up. Shelved it and bought a pfsense box for the internet and use a Ubiquity wifi AP.