Warning won't go away - "Multiple GoTrueClient instances detected"

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Hi, I’m working on a Next.js 14 project hosted on Vercel, using Supabase for authentication.
Despite implementing a singleton Supabase client using globalThis, I keep getting this warning:

Multiple GoTrueClient instances detected in the same browser context.
It is not an error, but this should be avoided as it may produce undefined behavior…

What I’ve already done:

  • Supabase client is imported only from lib/supabase/client.ts (singleton via globalThis)
  • No instantiations inside components or hooks
  • Server-side uses lib/supabase/server.ts (with cookies and createServerClient)
  • I cleared browser cache, localStorage, tested all flows (login, register, etc.)
  • Still happens on both v0.dev and Vercel preview deployment

The warning often appears during login/register or after page refreshes.

:red_question_mark: My questions:

  • Is this warning just a false positive in dev?
  • Is React Fast Refresh or Vercel’s SSR causing multiple Supabase auth calls?
  • Has anyone solved this cleanly in a Vercel + Supabase + Next.js 14 stack?

Thanks!