I’ve been experiencing exactly the same problem, and it was a total mystery as to what caused it until I saw your post. I’d tried all different methods for deleting viewed recordings but they just kept coming back.
After seeing your post I unplugged my usb drive and deleting has started working again.
I’m happy that I can fix this by just unplugging the drive. I wasn’t using it very often.
It’s just another one of the niggles about this particular box.
I don’t know what’s happened with this product, they seem not to want to release new software to address the many issues people have reported.
I personally quite dislike the EPG compared to previous Humax offerings, and find it difficult to browse for programmes.
Cheers,
Keith.