I have the exact same issue and I don't believe I've changed anything (famous last words) since it was working.
I've tried:
-Uninstalling/Reinstalling Reaper. Even tried a previous version of Reaper.
-Uninstalling/Reinstalling Helix Native. Tried previous versions of Native, but the "Show Details" under installation indicated that the installer found a newer "Core" file and I doubt it even installed.
-Deactivating/Reactivating Helix Native both online and inside Helix Native - I got it to run briefly (not sure what I did, maybe running the plugin as a separate process, but even that doesn't work now) and it then gave "Failed to Connect to DSP Engine. Error code 8201". Not sure exactly what I did to get it to stop crashing and load, but it still never worked even then.
-"factory resetting" Helix Native.
-System Restore - A full Windows 10 system restore to a backup point that for sure it was working on.
It's also an interesting piece of data that my authorized devices show two, one with Windows 8 and one with Windows 10. I've never had Windows 8, so no idea what's going on. Licensing software issues?
I put the vst3 file in the right spot, had it scanned, but in Reaper it's listed under the "Plugins that failed to scan", which makes me think it's Native.
If there are any log files that can help pinpoint the issue I'm willing to provide them, but this has me at a complete stand still on my music.
I've submitted a ticket to Line6 and will report back if I am able to remediate the issue.