API returning internal debug/test responses instead of actual content

Description:
Since Jan 29, 2026, our production application has been intermittently receiving 
what appears to be internal test/debug responses instead of actual generated content.

We're calling gemini-2.0-flash and gemini-3-pro-preview models, but the responses 
contain this format:

Say "connected" if you can read this.
connected
None

circle
200
Gemini 2.5 Flash-Lite
[timestamp]

Key observations:
- We request gemini-2.0-flash, but response shows "Gemini 2.5 Flash-Lite"
- This is clearly internal test output, not our prompts being processed
- Occurred 50+ times between Jan 29 - Feb 3, 2026
- Not related to API key rotation - same key, same issue before/after
- API key prefix: AIzaSyA5LQ...

This is severely impacting our users who see .... instead of AI content.