Hello Stuart, 

There is a peculiar issue which happens within our salesforce production org. Wanted to get your opinion on it. 

1. When we try to update a custom object through the custom API and a sales user simultaneously works on an Account which may be related to the custom object, we keep getting this error as part of the API response ""errors":[{"statusCode":"UNABLE_TO_LOCK_ROW","message":"unable to obtain exclusive access to this record or 11 records: "
2. This also happens when we do upserts on Account object which triggers rollups helper or process builder for the same object (row) which happens concurrently, and when we do upsert on Account object and end user also accessing the same row simultaneously. 

Is there a way we can handle these concurrent requests better and any best practice we can refer to avoid the "unable to lock row" error?