We're using Jira Cloud, with Company Managed, Kanban projects (Next Gen).
We're using Tempo for time recording. We had been successfully creating issues in projects until very recently, when we began getting the following error:

Problem is, I'm not able to find Original Estimate or Remaining Estimate in Fields when I go there to make them optional (Via Project Settings -> Issues -> Fields). We're using the System Default Field Configuration. In Tempo set up, Estimate is already optional.
Has anyone had this problem and found a solution? At the moment the workaround is to clone already existing issues in projects and edit them.