This might be a crucial experiment for us to know more about the trigger of AI stock purchasing/selling mechanism. Have you save and reload to see if AI always does this around the same time frame under similar circumstance? And do you know the tricks to artificially inflate or deflate your corporation's stock market value, and change around certain factor to see how it affects this odd behavior.
I have no doubt there's a lot of loop hole in AI stock purchasing/selling mechanism, since it's very easy to gain money on stock market. AI controlled corporation usually does quite well in earning profit. But individual person's stock purchasing/selling not so much. I find they do questionable transactions sometimes myself. Perhaps there's a mechanism (or lack of it) to make AI person behave differently and deliberately bad to make AI corporation perform better?