Try enabling IPSec passthrough, or relevant setting, on the AX6000. The setting can be found on the Advanced --> Nat Forwarding --> ALG page.

Silly question, but have you rebooted the router yet? I have had this happen many time with various routers and a reboot usually fixes it. Unplugging the power briefly and plugging back in is often...

Sometimes you need to reboot the modem first, then the router. What model Arris do you have?

My first thought is your switch went bad or is hung up. if there is a hard reset feature, try that. Otherwise, 8 port switches are pretty cheap these days so consider replacing it.

Try changing the wifi security settings from auto to AES (preferred) and TKIP. Some older devices (really old actually) may only connect to TKIP. Also, to rule out authentication problems, briefly...

Speeds advertised by ISPs are theoretical speeds. WiFi connections will struggle to approach those speeds and the quality of your ethernet cables can also play a part in achieved speeds. Also, ensure...