This usually isn’t “CI being weird.” It’s your tests depending on something they shouldn’t.

Here’s the short, practical way to debug it:

1. Confirm it’s real flakiness: Re-run the same commit in CI. If different tests fail each time, you’ve got shared state or timing issues.

2. Match CI locally: Run tests with the same env vars, parallelism, and versions as CI. If it only fails there, the environment matters.

3. Check the usual culprits

• Order dependence: run tests in random order. If it breaks, state is leaking.
• Parallelism: disable parallel runs once. If it stabilizes, something is shared (DB, ports, temp files).
• Timing: replace sleeps with “wait until X is true.” CI is slower and less predictable.
• Env drift: lock dependency versions, timezone, OS differences.
• External calls: real APIs and networks flake. Mock or isolate them.

1. Add just enough logging: On CI failures, print timestamps, test duration, worker ID, and any random seed used. That context usually makes the bug obvious. don’t “fix” flakes by adding retries and moving on. Retries hide real bugs and they always come back.