Subset of MERGE queries lead to setting unexpected property values

Update timeline

1. identified Mar 03, 2026, 09:35 PM UTC

   A recent update resulted in MERGE queries which referenced the same merged property on both the left and right hand side of an ON MATCH SET or ON CREATE SET clause deleting that property from the node, or setting it to an invalid value during query runtime. The node being matched against must have had at least one property uniqueness constraint present. A fix has been identified and will be applied as soon as possible. Instances marked as "Production" are not impacted.

2. identified Mar 04, 2026, 01:39 AM UTC

   The fix is being deployed and the status page will be updated upon completion of the full deployment of the fix.

3. identified Mar 04, 2026, 04:52 AM UTC

   The fix is being deployed and the status page will be updated upon completion of the full deployment

4. monitoring Mar 04, 2026, 02:07 PM UTC

   The fix has now been deployed to those instances impacted and we are monitoring the situation.

5. resolved Mar 04, 2026, 03:19 PM UTC

   The fix has been fully deployed to all impacted instances. This incident is now resolved.

6. postmortem Apr 08, 2026, 06:39 AM UTC

   ## What Happened An issue was introduced in the Neo4j 2026.02 release where MERGE queries that referenced the same property on both the left and right sides of an `ON MATCH SET` or `ON CREATE SET` clause could potentially delete that property from the node or set it to an invalid value during query execution. This behaviour was observed specifically when the node being matched had at least one property uniqueness constraint. ## How the service was affected A change in the Neo4j 2026.02 release introduced a potential risk of writes failing or invalid data being returned for queries using MERGE together with `ON MATCH`. This issue affected instances across Aura tiers and required immediate investigation by Neo4j Engineering. The team identified the root cause and deployed a fix in version 2026.02.1. ## What are we doing now The following proactive measures have been implemented to reduce the likelihood of similar incidents: * We have strengthened test coverage for `ON CREATE` and `ON MATCH` clauses, particularly those involving more complex expressions. * We are investigating additional safeguards to improve our ability to control MergeInto/MergeUnique behaviour more flexibly, as well as potential rollback capabilities to support recovery in future incidents