I'm fairly interested in the concept of the logic plague. As a broad-stroke denominator, it seems to refer exclusively to constructs that defect from the ideals of the Forerunner Ecumene. There is no true "infected event horizon" specifically pertaining to the Flood, as far as I can tell. Constructs displaying even a modicum of inclination or propensity toward subterfuge were dismantled on sight in the later years of the war. This leads me to believe that the logic plague, while codified by the [compound intelligence] in a major way, could just as easily be carried out by any number of individuals capable of pockmarking the ideals behind the greater Ecumene conquest. For example, were a construct to fall to the side of Forthencho based on its own whims - such as discovering a human imbued with a Forerunner Genesong, and opting to aid it, etc. - it would likely be demarcated as being "plagued" despite being an entirely willful, albeit passive, change of heart with truly benevolent intent. This strikes me as particularly noteworthy because the modern-day (2551+ era) UNSC also notes human [bureaucratic tactical] forces not in ideological alignment with their own as immediately belonging to an Insurrectionist front, or more disingenuously a United Rebel Front.
The logic plague seems like a similarly-geared "us or them" label. I highly doubt that a "healthy" Mendicant Bias, in its forty-three [year] conversation with the Gravemind of the time, could have a specific window of time pinpointed as its subversion into the [poisoned fount] incarnation of Mendicant Bias. Do you believe it's possible, by extension, that "logic plague markers" are not an [intendens de tenebris redivivus]; but instead a series of checks and balances, in equal parts, designed to prevent degenerate continuous thought on part of the construct resulting in "Rampancy," as well as a way to keep truly intelligent constructs - "Smart AIs," by human coinage - from defecting beyond repair? There seem to be extremely few Forerunner artificial intelligence programs similar in power and routine use as the UNSC "Dumb AIs," one-dimensional constructs built for a singular, usually repetitive, mechanical process. That alone could have saved a substantial amount of lives in the original war.