Well, let me share my versions from 2nd level IO and FBI.
I started calling them about 1,5 months after I had my 1st FP done, yellow letter received and hasn't been put in the Q for interview for some reason:
FBI: 1st FP were readable and results sent back to USCIS.
USCIS: everything looks great you should be receiving IL soon, btw have you ever been convicted of any crime? if no, then you should be fine
USCIS: Case received and pending - that's all the info there is there
USCIS: I don't know why you are not in Q, probably too soon, call in about 1-2 months for update. Background check on applicants continues een after they naturalize.
USCIS: No, you are not in the Q, your PD is in March and it's only end of June! Call in 6 months.
USCIS: No, you are not in the Q, you are asking why other people get IL much faster than you? Well, they are just luckier than you. We sent you a letter in March, you will hear from us again when your PD becomes current.
USCIS: Let me see, no you are no in the Q. Why? Seems like there is a problem with your FPs.

Just wait to hear from us about your next steps. No, I can't open a service request, just wait.
WTF??? After 3 months of calling and hearing everything is fine?
FBI: Oh yes, your FPs were not readable and therefore rejected.
Infopass: US citizenship is a priviledge. Yes, your FPs were rejected, we can't do anything about this, because your case is with NBC. Write them a letter. No, you should not be expecting 2nd FP letter right after your 1st rejected prints, we process I-751 and N400 differently and name checks, backgroung checks, FP checks are done differently.
USCIS 1st level: Opened a service request with NBC and sent a letter to their postal address as a back-up.
USCIS: My written letter was completery ignored, hovewer got a response to my service request in about 2-3 weeks. Turned out I never received 2nd FP letter from April and therefore my case was suspended. They mailed me a copy of missed (never sent, lost by USPS, misplaced whatever) FP and told me to reschedule appoinment.
After all that how can one not love them dearly?