Clean up log levels and log messages

Help me clean up the logs of a service so they help during an incident instead of getting in the way.
Service: [Service]
Problem: [Problem]
Usage: [Usage]
Steps: 1. Read the sample lines and the logging code and group the messages by purpose: errors someone must fix, expected exceptions, flow information and debugging details. 2. Propose a short rule for when each level applies, with one example from the material each. 3. Flag messages with the wrong level, such as expected rejections logged as errors or real outages logged only as info. 4. Rewrite vague messages like "an error occurred" so they name the action, the affected identifier and the cause, as fixed fields instead of free text. 5. Flag lines that contain passwords, tokens, full email addresses or other personal data and suggest shortening or dropping them. 6. Name the ten noisiest messages and whether they can be shortened, aggregated or removed.
Output: level rule, list of changes per message, new wording and a list of lines with sensitive data.

Take particular care to give every message a clear level and fixed fields and keep sensitive data out.

Before you answer, check: Are all instructions met? If key information is missing or a placeholder in square brackets is still in the text, ask instead of guessing. Mark assumptions as assumptions.​