I have a plugin with a number of fields in its config.jelly file, and I have corresponding methods to validate them in my Descriptor class. However, because the form apparently populates with empty or default values when it's loaded, requests to the server are sent for each field before the user interacts with the form.

If something slows the server's response time (a breakpoint in my case, but it could be something like a slow resource as well), the user can continue to interact with the form before the responses for those validation requests are received. Then when the responses are received, they're already out of date, meaning that an error message will be displayed for field values that are actually valid.