I NEVER use the aop to c/I, only aa.com; the only time I had an issue with OLCI was on an INTL itn that they didn't re-ticket properly, 15 minutes after calling AA I was able to OLCI.
Even mixed itns like JFK-LHR (AA); LHR-ZRH (BA) (all on one pnr), I can do OLCI and print both bps.
You might want to check to see if your passport number and expiration date are correctly listed in your profile on AA.COM.
app or website, same issue for me. Cannot check in. Outbound never any issues on check in at the counter. Return sometimes I get SSSS and get pulled aside. Most recently got locked in a room by myself for 2 hours in AUA.
definitely validated the passport data is correct. This issue has spanned 2 passports.
So dunno. Cest la vie.