I'm running Hazel 4.2.6. on macOS High Sierra 10.13.5. Rebooting the Mac doesn't help.
When I click the eye to Show Rule Status, I can see the following against the file:
. Could not import text from /Users/<foobar>/Library/Mobile Documents/com~apple~CloudDocs/00-Inbox/<foobar.pdf>.
I've had this rule running for at least a year without fail. To my knowledge, the format of the documents (password-protected PDFs) has not changed.
The files contain SPI and I don't want to share them with tech support, though I'd be glad to do anything else to help with troubleshooting.