Run this while the problem is happening, on the device and network where the plugin/customizations won't load. It checks, from your browser, whether app.sparkplugin.com is reachable — and if not, which layer is failing. It sends nothing anywhere; results stay on this page for you to copy.
running…
Press “Run the check”.
Test
Result
Time
Detail
Copy this and send it back
Two things that would help us most
Right now, without changing anything, open this same page on another device on the same Wi‑Fi and run it. Tell us whether that other device shows the same red result or works fine.
At the same moment, is your email (Thunderbird / mail app) also failing to send/receive? Yes / No.