Hi there Duncan, thanks for your question.
The 1809 update has been paused by Microsoft while they resolve some issues with it. Your issue may be related, so you can uninstall 1809 to revert back to 1803. Here are the steps:
-Click Start and type Update.
-Click "View installed update history".
-Click "Uninstall updates"
As you mentioned, if it's been more than 10 days since 1809 was installed, the only way you can rollback is a reinstall of Windows. So if you can do that, it will resolve the issue. Otherwise, you may need to hold off until Microsoft releases a fix for 1809.
Here's more information on the updates:
https://support.microsoft.com/en-au/help/446461...
Hopefully that helps! Please let me know if you need more help. Thanks!