I worked on a highly complex, high-volume automated procurement sourcing system many years ago. Each Purchase Requisition (PR) -> RFQ -> Bid Response -> Purchase Order could have many-to-many relationships, splitting & bundling at each line item (even the arrows above don't give the right idea, as things could go to re-bid, long-term contract with task orders, etc.).

We tried for nearly two years to get the status/state of each PR line item to update in real-time as events occurred during follow-on steps, but it was extremely brittle.

We finally added an intermediary queue and centralized all the logic in batch. Anytime something happened that might trigger a state (not verified), we tossed it in the queue. Then, we processed the queue every five minutes through a rules engine that was a classic factory pattern (a favorite anti-pattern). Every time the PR # ran through the rules engine, it would have a deterministic result. Sometimes it would pass through 10-20 times with no state change, but at least it was predictable.

We thought it would be too inefficient, potentially processing the same PRs 100s of times without any actual change to the state. However, the servers handled it fine, and it was real-time "enough" the users didn't notice a lag. We went from fixing issues several times a week to no changes for the remaining two years I was on the project.