system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] What did the two missing primarchs do to deserve censure from imperial records?

There were 20 primarchs created and scattered by chaos, and all 20 we're found, but some point between their discovery and the Horus Heresy, 2 of them managed to screw up so bad that they were completely removed from imperial records. This is a punishment even more severe than what the 9 traitor primarchs received after what is considered the greatest betrayal in the history of the Imperium.

The only thing I can think of more damaging than half of man's elite army falling to chaos is ideas, ideas that would dramatically alter the collective culture of all mankind, threatening what it is. What would these crimes be?

The only thing I can think of is that one may have somehow rediscovered how immensely beneficial AI can be, using it to great effect perhaps before he was discovered, the other may have landed on a world much more accepting of xenos, like an eldar exodite world or one where man trades and lives alongside aliens in harmony which the emperor would absolutely never accept.

What could be more heinous than taking half the army and killing the emperor with it? We know Horus didn't receive the same treatment, why did these two?
gpt
The Emperor did not like failure.

Perhaps they were simply defeated or killed in battle. He doesn't want to mess with the illusion of an unstoppable Primarchs so he wiped their failures and their names with them.