Okay, it is indeed the webview crash 
I鈥檝e filed an issue with electron for this a couple of weeks ago: Custom protocol + Origin headers/request crashes BrowserWindow/Webview 路 Issue #10314 路 electron/electron 路 GitHub
I thought it was related to requests and access-control headers, but it doesn鈥檛 look like you鈥檙e doing any. It鈥檚 for sure related to remoteStorage.js (taking it off the page and it loads). So that鈥檚 helpful.
And to be clear, this is related to the localhost protocol. So if it鈥檚 live it鈥檒l probably work. Just super not helpful for local development.
But this at least gives me something more to debug against to see if I can find more of the why as to this happening.