I'm guessing this plugin uses process.env.SPEEDCURVE_SITE_ID to know which URL to trigger the analysis for.
A the moment this plugin runs the analysis for every context (production, branch-deploy and deploy-preview) which seems redundant.
It might be better to limit the analysis only for production context.
See:
https://github.com/PerfBeacon/netlify-build-plugin-perfbeacon/blob/84795d829048166c464d181fba0e2a359cc172c0/index.js#L20