From what I saw HMPO say on Twitter, once your documents are signed for, they sit around until an employee is assigned to them, which I guess happens when they are nearly finished processing their allotted applications. It only updates when your documents are linked to your application.
Thankfully I only need my passport to use as photo ID for a job since the DVLA are a complete shambles with 6 months+ waits for a provisional license. I do need my passport by 3rd March, so far I’m hopeful.