Why is my 90-day registration still pending after 6 days?

I would cancel your pending application and resubmit. Carefully check the details of your submission ( beware of autofill if using a phone) and ensure that they are correct and match the information on your TM30 exactly. Also make sure that you don’t submit on a day that the immigration office is closed ( Sat, Sun or Public Holiday). You didn’t mention when your report is due but be aware of the window of opportunity for online submissions which I believe is 14 days before the due date to 7 days before. Approval for online submission is normally within 24-48 hours in my recent experience.

Submitted 13 Jan, rejection arrived today. Never been rejected before so its a 3 hour drive to Immigration CM - thanks.

I guess you have to go there. I had it once where it took 4 days and was rejected by system. Officer told me that sometimes it is not working and they didn’t get the notification.

I did mine online on Monday morning. I received the confirmation a few minutes later and the approval late in the afternoon on the same day. It's never taken more than 24 hours for me. I would try submitting it again.

You're clearly talking about 90-day reporting.

As long as you are applying inside the window of opportunity, which now appears to be from 2 weeks before the due date until 1 week before the due date, you should be fine and just wait it out.

Remember the first time you apply after you come back into the country has to be in person not online.

Not much you can really do, maybe call the immigration hotline (1178)and see if they can help but other than that you just have to wait.