This is not unusual.
Background checks vary wildly in how quickly they run to completion, and it seems that in the aftermath of the massive influx of applications there has been a slowdown.
IRCC's commitment is that they will complete 80% of all applications within 12 months. Some people will get their citizenship early, while for some it will take closer to the 12 months (and for a few it'll take longer than that). There is no way to expedite that process; the only way to make things go as quickly as possible is by responding swiftly when they ask for information. You've done that, so now you can do little but wait.
You can ask for your case notes, but doing so will not expedite the process, nor is it likely to tell you much. It may identify that it's the security clearance that is still pending, which is the likeliest reason for the delay. It's also one you won't be able to find out more about, as CSIS -- the agency that does those checks -- no longer releases process information.
People on the forum will refer to those notes as GCMS notes, for the case management system IRCC uses, or ATIP, for the law under which the request can be made. If you were to make a request it would be under the privacy regulations rather than access to information, as it pertains to information about you (the difference is that privacy-based requests are free, the others cost at least $5). I don't believe it useful to request them (certainly not for applications that have not gone near or over the 12 month mark). And it's just more work for IRCC to do.
