Fast speed on two computers (480Mbps) slow on all others, phones, etc. (96Mbps). RBR850, RBS850

I just purchased an RBR850/RBS850 setup. Everything seems to work, but only two wired computers get fast 480Mbps speed, whil EVERYTHING else, computers, phones, tablets, etc. get slightly less than 100 Mbps. On my previs setup with two router, I have fast speed on all devices. What gives? I have tried LOTS of solutions. Even hardwiring a computer directly into the main RBR850 gets a slower speed. Please help. This setup was spposed to be state of the art. It is worse than the 10 year old setup it replaced.