Queries using the new vector index fail or return no results because index state is POPULATING (not ONLINE). Other queries may slow down due to high CPU/IO from background population on large datasets. Index creation command succeeds but progress stalls (e.g. at 14%).

Neo4j schema indexes (including vector indexes) are populated asynchronously after CREATE statement succeeds. During POPULATING state, the index is unavailable for queries but database remains operational. However, for large datasets, population can be slow/resource-intensive, appearing to 'block' as it consumes CPU/IO heavily. Schema lock acquired briefly during CREATE; population uses background resources but can contend if under-resourced. Hangs may occur due to resource exhaustion or bugs fixed in later versions.