You are kinda out on you own. Rarely seen PC hardware here and you have a problem running an old unsupported Pro Tools version.
You made a decision to buy new computer hardware and risk running an incompatible systems, you might need to look at monthly rental of Pro Tools Ultimate, some way to get on a supported system. Maybe sell the HD Native hardware.
You enable Ethernet and WiFi and see a problem. Disable it and works.. that does not prove your system is "OK" and it's a specified WiFi or Ethernet related thing you might be able to fix... they may just be the little latency causing problem that pushes you over the edge. WiFi is notorious for doing that. Or maybe it is a specific issue with your hardware who knows... you can exclude that by swapping hardware etc. but I'd do that after getting everything else into a supported configuration and running down all standard troubleshooting.
Is the system *fully* optimized? Every last thing done?
Have you done the basic troubleshooting in the KB for HD Native errors?
https://avid.secure.force.com/pkb/ar...ve-errors-9071
Have you done any basic other troubleshooting? Trashed prefs? Removed all .aaxplugin files? etc.
But ultimately getting yourself onto a supported setup is excellent advice.
Especially because Pro Tools AAE was mess for CPU related issues for many users, there were significantly improvements in 2019.5. And... you are having CPU errors on Pro Tools 12.x... getting beyond 2019.5 would be a priority for me. And I don't care at all that you had it working before. You changed hardware and are now seeing a CPU error that has hit lots of users especially on 11/12/2018, with lost of underlying causes.
But again if all that does not work then you are likely on your own, other users here are not going to be too interested in trying to help you out of a mess you have gotten yourself if you're not going to be on a close to supported configuration.
And even on Pro Tools 2020.x look up the advice on DUC for setting CPU affinity on Windows. Lots of threads about those extra optimizations for Windows.