It is found that we are getting race conditions when calling issue updates via PUT /rest/api/2/issue .

We are using the format of update with add to add components to an issue, but are finding that concurrent requests can cause subsequent requests to override and therefore ‘delete’ components from the earlier requests (ie, Request 1 -> add a, Request 2 -> add b , Request 2 also deletes a if the requests are timed closely to each other).