Does the book in question open with koreader as default when you click on it from the Pocketbook library?
If not, long-press on the book and choose:
Open With > koreader.app
Then reboot your device. Once rebooted select the book from the pocketbook library again and make sure it starts with koreader. Then see if progress bar is being updated.
If it still isn't working after this then I'm afraid I'm out of ideas.
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