litellm - 💡(How to fix) Fix [Bug]: Admin UI stuck on loading spinner (v1.83.10) - Next.js hydration fails

Bug Description

Admin UI at /ui/ loads HTML successfully (HTTP 200) but JavaScript hydration never completes - stuck permanently on "🚅 LiteLLM" logo with spinning loader.

Environment

• LiteLLM Version: 1.83.10 (main-stable)
• Docker Image: ghcr.io/berriai/litellm:main-stable
• Database: PostgreSQL 16
• Redis: 7
• OS: macOS (Docker Desktop)

Reproduction Steps

1. Deploy LiteLLM with Docker Compose (PostgreSQL + Redis backend)
2. Set UI_USERNAME, UI_PASSWORD, LITELLM_MASTER_KEY
3. Access http://localhost:4000/ui/
4. UI shows loading spinner indefinitely

Observed Behavior

• HTML: Returns 200 OK with BAILOUT_TO_CLIENT_SIDE_RENDERING template
• Static assets: All JS/CSS chunks at /litellm-asset-prefix/_next/static/ return 200 OK
• Login flow: POST /login → 303 redirect → cookie set correctly (JWT with user_role: proxy_admin)
• API: All API endpoints work correctly (/user/info, /v1/models, etc.)
• Client-side: JS loads but never hydrates - no subsequent API calls observed in server logs after UI HTML load

Server Logs (sanitized)

INFO: "POST /login HTTP/1.1" 303 See Other
INFO: "POST /ui/?login=success HTTP/1.1" 405 Method Not Allowed
INFO: "GET /ui/ HTTP/1.1" 200 OK
# No further API calls from UI client

Cookie Response

set-cookie: token=eyJ...; Path=/; SameSite=lax

• No HttpOnly flag (JS can read)
• SameSite=lax
• JWT contains valid user_role: proxy_admin and session key

What I Tried

• Set PROXY_BASE_URL environment variable
• Removed LITELLM_LICENSE
• Disabled STORE_MODEL_IN_DB
• Patched Prisma budget_limits query errors
• Tested with main-latest tag (v1.82.6 - same issue)
• Verified CORS headers (access-control-allow-origin: *)

Expected Behavior

UI should hydrate and display the admin dashboard after loading.

Additional Context

• Login page (/ui/login/) also stuck on same loading spinner
• API works perfectly - can manage keys, view models, check spend via curl
• Issue appears to be in Next.js static export client-side hydration, not server-side

Possibly Related

• #11531 - /ui is not accessible
• #12226 - Fix rendering ui on non-root images