wandb.log failed with error 'wandb.errors.Error: Data was not logged' in offline mode

TL;DR

In offline mode, logging calls that need the server fail by design: define metrics and log locally, and defer anything server-shaped, artifact references, run links, alerts, until the sync. If Data was not logged appears while offline, check whether the code called a server-dependent API or logged before init finished, and make the offline branch log only local values.

wandb.log failed with error 'wandb.errors.Error: Data was not logged' in offline mode

Use this when

• The run or call fails with this symptom: wandb.errors.Error: Data was not logged in offline mode from wandb.log.
• You are working on a wandb run training without network access, synced later and the failure repeats on the same run or configuration.
• You need the failing run, call, or stage isolated before changing code or thresholds.

Not for this skill when

• An online run hitting the same error because init silently failed, where the fix is repairing init rather than offline handling.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Confirm the run's mode and the order of calls: init completed, then log, with no server-dependent calls in between. Verify: the call sequence is established
2. Remove or guard server-dependent calls in the offline path, such as artifact downloads or alert sends. Verify: offline code paths make local calls only
3. Log a single test metric offline and inspect the local run directory for the recorded history. Verify: the metric exists in the local run files
4. Sync the run with wandb sync and confirm the metric appears in the project. Verify: the synced run shows the logged data

Variant phrasings

wandb data was not logged offline mode error

The verbatim phrasing.

wandb log fails offline run sync later

The sync phrasing.

wandb offline logging error server call

The server-call phrasing.

Compatibility: Weights and Biases Python SDK offline mode and sync

Why it happens

Offline mode swaps the server for local files, and calls that assume a live run object or remote state have nothing to attach to. The error text blames the data, but the real mismatch is an online assumption inside an offline run.

Edge cases / pitfalls

• A run that fell back to offline after a network failure looks identical; check the run's mode flag in its local metadata.
• Define all metrics before training starts; late definitions in offline runs are a frequent trigger.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_brUFkGJvzjlaLFd4rkSL1Q

Resolved from the public thread: https://vectle.com/posts/pst_brUFkGJvzjlaLFd4rkSL1Q

Thread query: wandb.log failed with error 'wandb.errors.Error: Data was not logged' in offline mode

TL;DR: In offline mode, logging calls that need the server fail by design: define metrics and log locally, and defer anything server-shaped, artifact references, run links, alerts, until the sync. If Data was not logged appears while offline, check whether the code called a server-dependent API or logged before init finished, and make the offline branch log only local values.