I believe the hidden part of the fall is the nature of Exsurgency. The public knows that the TITANS employed various nanoplagues and viruses, but do not know how potent Exsurgency is (most of them anyway) or various effects like psi. I'm not sure even Firewall or OZMA knows the true nature of the Exsurgency either though. They sure don't know about the probe. (Maybe some really high-rep ones know, but they aren't talking at all)

I guess that it depends on who you ask like everything in EP. For example: If uoi ask a Jovian he will say that the problem was the unresttricted progress on AGI development and thats why we all should stop this reckless progress or the TITAN event will repeat. If you ask an anarchist(it doesn't matter if he is anarcho-capitalist, anarcho-syndicalist or wathever variant) they will say that it was caused by goverment actions being bad for everyone as usual. If you ask a Mercurial they could say that it was the destructive nature of humanity that resulted in the need of TITANs. For ultimates it was the decadency of the collectivism that lastrated all humanity and made it weak for the TITAN attack since the TITANs used mostly the very own weapons humanity already had to exterminate them, and I guess that for them when your weapon is more powerfull than you, you simply don't deserve to exist. And so on, maybe the planetary consortium have a distinct way to see it, like it was only a smal mistake of "those" old Earth goverment but hypercapitalism with ciberdemocracy can avoid this to happen again, and everybody will be happy again with a slight different flavor of goverment. In any case, the thing is that the TITANs are well known, maybe you can play with other names like simply "a seed AI" or "the reapers"(ha! take that mass effect reference!) but it was non human and created by us, and it completly obliterated all human life on earth. All the stories about monsters, nanotech and things like that are more into the legends and promoted by survivors but no one would believe in such fairy tales like the classical conspiracionists. I mean, would someone believe claiming that he saw monsters going throught walls and eating people without a mouth? No, they would say that he/she was nervous and couldn't think clear in that moment, maybe that was only optical illusions or maybe she hit her/his head so bad that had pretty interesting dreams and thats all. What will be next? hive-ameboidean Alien species that conveniently appear after the fall and trade with transhumanity? Oh way...

It was the only location where the final part of the recall code OPE was stored

I think one thing to note is that some of the information is not necessarily clear; for instance: Average people might know about the TITANs, but not know exactly how they functioned (or that they were ASIs, instead of, say, AGIs) or really know anything about their origin (i.e. North American military). The exsurgent virus is not well understood to the public (certainly not the details about the four strains and its digital/biological/nanoswarm vectors being one and the same), and at the very least xenomorph strains and asyncs are repressed information. The other "secrets" actually seem pretty secret to me.

I bet the Planetary Consortium would blame the old national governments deliberately building autonomous second-strike "Solomon protocol" systems, beginning with the Soviet "Dead Hand" during the first Cold War. Obviously, when two of these are pitted against each other, Bad Things happen.