tried all of these things, and appear to be in the same boat as you - further, when I try to change to CAPS in my Qantas account - it already appears that way in the 'My Profile' page.....grrrr
I've tried multiple devices now and can't find the link to register - after having similar issues to Pushka - trying the PDF certificate, and name matches.
The premium entry was closed last week on Wednesday when the business lounge re-opened for the first time, and the Q Club opened for the 747 farewell joy flight.
The lines at security were short, although they have a couple of body scanners installed now.
It was opened specifically to accommodate the pax for this flight - I believe only the business lounge will remain open for the time being - QP pax can use the business lounge while it's the only one open - pending headcount and social distancing rules.