Although our diagnostics may show everything working properly, when a third party router is used, the only thing we can test is up to the socket point.
But let's see if we can find a solution going by the system of elimination. Do you still have our router stored? It's default is entirely set up to support our service and if you need a router model update, we can check and provide, free of charge. Compare how it goes with our router connected, versus the Asus router you invested in, speedtest and practical use alike, then feel free to DM us to let us know!
If you notice any differences, we'd suggest chasing ASUS support.
We hope this suggestion helps!