AC3000 RBK50 - iPad Pro WiFi connection issues

I have same issue (after a day or so looks to be connected, but is not connected) with iPad Pro 9.7 inch. Don't have the issue with the older iPad Air or newer iPad Pro 10.5 inch. I'm running the same firmware as you 2.1.2.18. I actually have a replacement ORBI router as the previous firmware to this one caused high CPU use on ORBI routers and made my original unit purchased in November 2017 a brick. While I was waiting for my replacement unit to ship, I picked up an inexpensive WAP (different vendor) and used that behind a business class router to run my wifi and it works flawlessly with all my Apple devices. Now that I am outside of 90 days, Netgear sent me an email that I have to pay to speak to them for support. The inexpensive WAP that I purchased coexists fine with the ORBI, so my solution is to keep my iPad Pro 9.7 inch connected to the inexpensive WAP, and use the ORBI as a WAP only for everthing else.