A PC reboot is required to release documents to print.

[lookingforsolut]

Documents don't print unless I reboot the PC, and that triggers releasing them.  I have run HP Scan Doctor numerous times and it says all looks fine.  Documents can't be "restarted" or "deleted".  BTW, I just noticed that that documents that were sitting there waiting to print since yesterday are now gone.  Based on recommendation from HP Dashboard to download a more comprehensive driver I did this morning (28.1.1328.1) and I wonder if that clobbered the documents I wanted to print somehow.

[Repairatrooper]

If you installed a driver while there were documents in the queue then you likely lost them. If this new driver does not resolve the issue I suggest that if you are connecting to the printer via network, you ensure that you are using a standard TCP/IP port for the driver and not a WSD port. I have found WSD very problematic in that printers that go to sleep can go offline and only a reboot refreshes the driver properly.

[lookingforsolut]

Thank you Repairatrooper for your post.  After installing the new driver, so far so good, it looks like all documents are printing. Not 100% sure yet, but looks promising.   Previously some printed right away and some didn't, with no discernible pattern to guide me as to the reason why.

Regarding network, TCP/IP, WSD, this is just a simple wired connection from laptop via USB cable.

I think you are right, the new driver wiped out the pending documents that had not printed yet.

Observation: HP Print and Scan Doctor had some value, to run a scan and perhaps rule out some possible problems, but it seemed to indicate my previous driver was up to date, whereas some other HP tool and message directed me to download a different driver, which judging by the date and number was much newer than the one I had installed which had been said to be up to date.  I also noticed that a couple of the links for Scan Doctor (5.7.4), didn't exist, and said "Page Can't Be Reached" when clicking on the links for Support & Troubleshooting, Software Drivers & Downloads.  I just tried running it now, and although it identifies my printer it gets stuck after that each time I try, and won't show the results of its diagnostics like it did previously, before I installed the newer driver.  So maybe the different HP diagnostic tools and drivers aren't compatible.  But if printing is working OK I won't keep trying to make the Scan Doctor work.