Juho Sarvikas explained the delay in a tweet. It seems that some certification issues needed to be cleared, and the developers are now doing a final round of testing before the stable software comes out.
#Android Pie 🥧for #Nokia 7 plus met with a couple of tricky platform specific certification bugs. We’ve got them now and are running final round of tests for quality assurance. Apologies for the delay. Like you know from Beta Labs, stability is there #nokiamobile
Juho Sarvikas (@sarvikas) September 26, 2018
This means that the Pie OTA update could arrive right on schedule or worst case scenario – at the beginning of the next month. It’s better to wait a little longer for all the issues to be ironed out than a half-baked release, right?