In which application are you viewing the exported pics?
Please try and change the Image format to jpeg and check if it allows you to select the created watermark and export.
Let us know if it helps.
They are JPG exports.
Many and varied. Everything from Windows builtin viewer to online apps.
Be aware that many browsers, including the Windows File Explorer, use the thumbnails embedded in JPEGs and TIFFs to show you thumbnails (even large thumbnails). LR has a long-standing bug where the watermark is not included in these embedded thumbnails. So File Explorer and other browsers won't show the watermark. You have to open the image in a "viewer" to see it at full-screen size to determine whether the watermark is there.
But it sounds like you've done that, so this isn't your problem. But as you troubleshoot, it can cause confusion.
And to clarify ... it used to work just fine and I only ever used to view the exported images at full size prior to placing on my blog. As I say, it appears to have stopped working when I moved to the CC version from the standalone app so perhaps some setting somewhere... like a registry key or some such.
Can anybody else offer an insight to this?
If not, what are my next steps to get this working again? Is it a complete uninstall which I really don't want to do ...?