Firmware 1.0.0.64 and nighthawk xr1000

What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?
Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended. 

Would need more information about the problems your seeing with wifi connections before thinking this is a FW issue. Not everyone sees same issues you may see. 

What devices do you have connected? 

What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and 40 to 48 channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

Has a power off for 1 minute then back ON with the ISP modem and router been performed since last update?
Be sure to restart your network in this sequence:
Turn off and unplug modem.
Turn off router and computers.
Plug in and turn on modem. Wait 2 minutes for it to connect.
Turn on the router and wait 2 minutes for it to connect.
Turn on computers and rest of network.

Has a factory reset and setup from scratch been performed since last FW update? A complete pull of the power adapters for a period of time after the factory reset then walk thru the setup wizard and setup from scratch. Recommend setting the default DHCP IP address pool range to the following after applying and a factory reset: 192.168.#.100 to 192.168.#.200.

I saw no wifi issues with my XR1000 when I had it online last year with this version of FW. Ran great for me:

https://community.netgear.com/t5/Nighthawk-Pro-Gaming-Routers/New-XR1000-Firmware-Version-1-0-0-64-Released/m-p/2271533/highlight/true#M31806

So here's a detailed run down of events:

- set up the new router and it went through a firmware update

- very erratic wifi with multiple devices including my phone and partners phone not being able to connect. It would sometimes work and it would sometimes not. 

- I thought i had got everything set up fine and then i activated smart connect before heading to bed and at 3am got awoken by one of my smart device notifications saying it's offline.

- checked the router and something went haywire, seemed to do a factory reset of itself or something. 

- i use the pin, did factory reset, reconfigured again and then was able to connect most of my smart devices and thought that was done but next morning, i hear another alarm from my security cameras which are on Lan connection and see that they're offline. Not able to get an IP and i can't seem to connect to the wifi on 2 x phones, ipad, alexa... etc. 

- I put my old wireless router back and everything works fine so to me this tells me it's the router. 

- I then do a factory reset and can't seem to connect again to the wifi so i call netgear support. 

- Netgear support tell me to roll back the firmware and that it's a known issue and they have tech's working on the update, however i believe this was just words to stop me from refunding the item. 

- Since rolling back the firmware, everything has been running smoothly with no issues at all so with all the steps taken, i feel it's pretty clear it was the firmware. I thought i was going mad as i just couldn't explain this erratic behaviour