Connectivity issues between RAX75 WIFI routers (2) and FVS318Gv2 Firewall//router/switch

Greetings.
Disclaimer: I am not IT savy like you all but do have some knowledge to handle simple settings. (I have also posted this request unter the FVS318Gv2 Firewall/router/switch model forum.
I have continues connectivity issues with my Nighthawk RAX75 WIFI routers (2) which are connected via Cat6 cables to a Netgear FVS318Gv2 Firewall/router/switch which is connected via a Cat6 cable to a Spectrum Hitron Technologies E31N2V1 router.
The FVS318Gv2 has an IP of 10.23.23.10 and the RAX75 WIFI routers have an IP of 192.168.1.1 & 192.168.10.10 and are each DHCP enabled.
I have called Netgear Tech support and Spectrum to no avail.
The firmware of the FVS318Gv2 is 4.3.3-6. The router refuses to accept the latest supported firmware of 4.3.5-3-.

I understand Netgear no longer supports the FVS318Gv2 Firewall/router/switch. I am seeking help in troubleshooting the connectivity issues.
I also would like to know if it would be easier to replace the FVS318Gv2 with a new switch and if so what model should I replace it with. I would prefer 8 connection ports but could do with 6.
Any help and suggestions would be greatly appreciated.

Respectfully,
Yves