In HELP-81692, we observed several clusters attempting to upgrade to FCV 8.2 while an index build was in progress. In such cases, the setFCV command fails with a BackgroundOperationInProgressForNamespace error. This error is transient: once the index build finishes, rerunning setFCV succeeds and the upgrade completes normally.

However, once a setFCV command has failed, there is no straightforward way to determine whether the upgrade is still in progress—other than by rerunning setFCV or inspecting currentOp.