I have a client who has noticed that some activities that they create are being duplicated. I can see solid evidence of exact duplicates - apart from the id in the activity record. In the activity table the 2 ids are consecutive, in the activity_contact table they are almost consecutive. The contents of the activity records are exactly the same - the created_date and modified_date are the same time to the second. The client creates a lot of activities - there are about 220K activity rows and they do have quite a few users working simultaneously updating Civi. This seems like a bug to me - any suggestions as to what else the problem might be? This installation is running 5.13.5 with Drupal 7.67
Not sure if it's the same problem but it could be the submitOnce problem which has a temporary fix in 5.14.1 and a fuller fix pending but is an easy change you can make:
i.e. remove the "submitOnce" line.