What causes Connection errors when refreshing from semantic models?

Transient network instability between the refresh engine and the Analysis Services endpoint. Complex queries involving multiple outer joins that hold connections open too long, causing the server to drop them. Gateway misconfiguration or overload causing intermittent connection drops. Schema changes across multiple tables submitted outside of a single transaction, leaving the model in an inconsistent state

How do I fix Connection errors when refreshing from semantic models?

Step 1: Retry the refresh manually — transient network errors often resolve on the next attempt without any configuration changes.. Step 2: If the error recurs on queries with multiple joins, wrap the outer join table in a Table.Buffer() call in Power Query to cache the result and prevent connection timeout.. Step 3: Verify that any multi-table schema changes were submitted as a single transaction using Tabular Editor, not Power BI Desktop, which cannot batch multiple table changes together.. Step 4: Check gateway health and logs in the Power BI admin portal to rule out resource contention or network instability on the gateway host.. Step 5: If the error persists across retries, open a support ticket with the RootActivityId from the error details to allow Microsoft to trace the session.

High severityconnectivity

Power BI Refresh Error:
Connection errors when refreshing from semantic models

What does this error mean?

The Analysis Services connector throws 'The connection either timed out or was lost' during semantic model refresh. This is typically a transient network failure, but can persist under specific query or load conditions.

Common causes

1Transient network instability between the refresh engine and the Analysis Services endpoint
2Complex queries involving multiple outer joins that hold connections open too long, causing the server to drop them
3Gateway misconfiguration or overload causing intermittent connection drops
4Schema changes across multiple tables submitted outside of a single transaction, leaving the model in an inconsistent state

How to fix it

1Step 1: Retry the refresh manually — transient network errors often resolve on the next attempt without any configuration changes.
2Step 2: If the error recurs on queries with multiple joins, wrap the outer join table in a Table.Buffer() call in Power Query to cache the result and prevent connection timeout.
3Step 3: Verify that any multi-table schema changes were submitted as a single transaction using Tabular Editor, not Power BI Desktop, which cannot batch multiple table changes together.
4Step 4: Check gateway health and logs in the Power BI admin portal to rule out resource contention or network instability on the gateway host.
5Step 5: If the error persists across retries, open a support ticket with the RootActivityId from the error details to allow Microsoft to trace the session.

Frequently asked questions

Will retrying the refresh automatically fix this error?

In most cases, yes — this error is classified as transient and a single retry typically succeeds. If it fails consistently across 3 or more retries, investigate query complexity and gateway health.

Why can't I use Power BI Desktop to batch my schema changes?

Power BI Desktop does not support submitting multiple table changes as a single atomic transaction. Use Tabular Editor instead, which allows you to stage all table modifications and commit them together, preventing partial updates that can leave the model in an inconsistent state.