In round 3 there was no event at the end of the turn. (I didn't think this was possible.)
This is possible. For example if there is a sunspot activity and nobody has any energy, or if there is a planetary pest and nobody has any food exploitations. The same rules as the original Mule, events that do not apply to anyone will not happen.
Also the AI displayed very unusual behavior....
The AI's behaviour depends on what happens in the game and is also partially random. It can decide to do unusual stuff, that's normal. For example if there is a high risk of pirates it can decide to sell crystite for a low price. The AI has not been changed in any of the later updates though, except fixing the reset of assay results between games.