Issue Summary

If an import is in the "handling missing objects" phase and is cancelled, the cancellation does not work and the import will continue processing all remaining work.

Steps to Reproduce

1. Create an import, e.g. CSV with a large number of entries.
2. Choose the "update" or "remove" option for missing objects on the object type mapping.
3. Run the import to create all the objects.
4. Update the import file so that there are very few entries left, meaning most objects will be considered "missing".
5. Run the import again, and wait until the "Handling missing objects" phase is reached (as displayed by progress in the UI) and cancel the import.

Expected Results

The import stops immediately.

Actual Results

The import continues processing all missing objects before stopping, without checking if it has been cancelled.

Workaround

Restart the customer's instance to kill the processing. No known user-driven workarounds available.