"It works now" is not a handover. You get the fix and the reason, so the same class of failure does not come back under a different name.

What I usually find: a Code node that works on one item and breaks on an empty array. A response the workflow parses as valid when it is truncated, which is the silent partial success and the worst failure mode there is, because the run reports success and the data is wrong. Authentication that expired, with the workflow failing every hour since and nobody watching. Data mapping that is correct for the test payload and wrong for the real one. A webhook receiving duplicates with no idempotency key.

How it works: you send the workflow export and a failed execution. I tell you what is wrong before doing anything, so you can decide whether it is worth fixing. Then I fix it, test it against the case that broke it, and write down what changed. You get the before and after JSON, so nothing lands in your instance that you have not read.

Self-hosted n8n in Docker is my daily environment, not something I read about. I maintain 50+ production workflows on my own server, so the failure modes above are ones I have found the hard way.