Status of citizenship applications that is not acknowledged yet

[mentalmind]

There is a huge backlog for citizenship applications for 2021, I believe nowadays they are sending acknowledge letters for applications that got received around August 2021 (totally my observation, no official info). My question would be, for the applications that get their passport back with missing acknowledge and missing payment receipt. Does it mean application is accepted but not processed yet or is there a possibility of application to get instant refusal still? (Like 6 weeks continuous residence rule not met, or wrong form is sent, or not enough resident days in calculator etc)

So I am wondering are we just waiting for the letter for application to get official or is there still possibility/risk of instant refusal? I know final decision might take 23 months or so, just asking for the instant refusal reasons that I mentioned above.

Would anyone have any info about it?

[OneWorld2122]

Not an expert but as per the official website :

Also, in exceptional circumstances, such as the Covid-19 pandemic, there may be delays in acknowledging receipt of applications.

However, once your application form is processed, we will send you an acknowledgement letter confirming your Application Reference Number and will include a receipt for your Application Fee of €175.