Galaxy A9 Phones having issues with Wi-Fi

[Panc]

Rather perculiar this one. Both of my parents seem to be having issues with there phones constantly disconnecting from the Wi-Fi in our house. The setup for the wifi is one netgear XR1000 router and a Netgear Wi-Fi extender running upstairs. This is setup to be a "Mesh" network. All other devices haven't had any issues other than my parents phones. They come up with a few different errors like "Couldn't get an IP address" or "Couldn't authenticate" etc. I have reset the network settings on both phones multiple times, cleared the cache folder by launching into recovery mode (Again on both phones), forgetting the network and trying to reconnect and the phones will both (Most of the time) refuse to reconnect to the network. other devices are still fully functional and both phones are fully up to date. Does anyone have any ideas?

[5xsavvy]

Maybe the "setup" may be the issue???