the changeset upload is known to take quite some time for larger changesets, sometimes resulting in timeouts and unclear overall status. Luckily, JOSM already covers some of those issues via its chunked upload, still there's always room for improvement.
Test period ended
Thank you for your interest. The test period on a dedicated server has come to an end. There will be a separate announcement once this feature is available again for testing. Thanks everyone for participating in the tests!