Nighthawk R8000 and Triband Extender device connection issues

[Simbro]

Help!  Having had a stable network setup for 4 years without issue, it is suddenly experiencing connection issues, where devices no longer connect or regularly drop their connection.  I have a nighthawk router connected to a 1GB modem in the basement and then 2 Triband EX8000 extenders, one on the ground and one on the first floor.  They are all set up for the same network.  The ground floor one first started having connection issues where devices weren't seeing it any more.  I restored to factory settings but it doesnt seem to have made a difference.  Rebooting temporarily helps, for hours, or days, but some devices seem to need to have their network access reset and then still lose it again.   For example 3 smart camera connected to it all lost connection today, rebooting the extender and two have rediscovered it and now work, one remains unconnected.  Ipad didnt reconnect and needed to forget and rediscover network to work, phone continued on fine!?  Also the smart TV is connected via LAN, and even that connection now drops briefly from time to time! I keep finding devices that are not working that have previously been connected without issue - lights, smart scales etc.  Also the nighthawk app that has worked fine, now fails to connect to the router to be able to troubleshoot.  Any ideas as hugely frustrating?  Doesn't feel like a hardware issue, but I have made no changes to the setup unless there was an auto firmware update that broke something in the last week or two?  All I can think to resolve is to replace hardware, but not sure where to start and which part might be the issue, so could end up replacing all and find it is a connected device causing it.  Help!?

[Valkrey]

check the firmware in you R8000.  The last firmware that was stable is 

Firmware Version
V1.0.4.68_10.1.75