This is a data integrity problem — a customer logs in and sees someone else’s order. It almost always follows a migration, backup restore, or staging-to-live push.
The scenario: Live site has orders up to #123. You restore from backup where last order was #110. Site continues taking orders: #111, #112. Then you import lost orders from live. Old order #111 overwrites new order #111. Customer B now sees Customer A’s data.
Sequential order number plugins make this worse by adding another mapping layer that diverges between environments.
Resolution requires database-level work — identifying conflicting IDs in wp_posts and wp_postmeta, checking timestamps, and manually correcting associations. This isn’t fixable from the WooCommerce admin.
Prevention: Before any migration or restore, note the highest order ID. After, verify no overlap. Never import orders into a live site without checking ID ranges.