Unfortunately, if it's not reproducible, there's not much I can do. If you want to "force" a bit of testing, you can delete a recent delivery (not marking as complete!) and do a full refresh. If the delivery doesn't come back including status messages, the request failed.
Should you be able to reproduce it, you can enable Settings -> Privacy -> Developer log, reproduce the issue and then send a problem report (Left menu -> Three dots -> About -> Report problem). Afterwards make sure to disable Developer log again as it creates huge log files.