Do you mean you are using Render Studio from RDNA to add the AO?  If so. the advanced AO script has issues with materials that already have an AO node plugged into them sometimes.  No clue why, I am not a material room guru, just know I have run into it a time or three.   I have Aikobot on my storage drive will have a look when I get back from taking my little ones to school.  Guess I'll need to reinstall A3 too lol.