I have seen several types of strange AI behavior in the games I have played with the 4.0 opt-in.
The first one is the AI seems to aggressively build way too many colony ships and constructors. They don’t have a use for them most of the time, so they accumulate. Then, when they find a place to use a constructor, all of them get sent there. The result is this.
A similar result is obtained with colony ships.
Both result in a waste of administration points, and the colony ships also result in a waste of population that could be put to good use on planets already colonized. The ships will stay there forever unless the AI finds a new place to use them. Notice that the Thalan planet is completely blocked.
Another problem is that the AI seems to forget about some of its ships for a number of turns. This applies to all types of ships, but it is especially bad when it happens to military ships during wars. There seems to be more wars in this version, so all the AI have a lot of ships doing nothing for numerous turns. I’ve seen ships moving like they’re going somewhere, then they stop and do nothing for numerous turns. They ignore everything around them. I have been able to avoid losing a planet by getting a fleet moved to the planet to destroy an attacking fleet that decided to just stop and do nothing just before it got to my planet.
This doesn’t happen to all ships all the time. It’s just happens to some of them some of the time. When they aren’t going to sleep they are very good at what they do, especially military ships. I lost four planets in a short period of time when my enemy's ships were working. Fortunately, they decided to go to sleep and I was able to get ships and transports there to destroy the enemy ships and take back my planets.
In one case, the Measured declared war on me, so I used the Prenumbral Beacon artifact to call a space monster to their home star system. When I managed to get some fleets there 13 turns later, I found this.
The space monster was still there, the Measured had plenty of fleets, and they were all doing nothing. I destroyed their asteroid mines, and they did nothing. I stayed there a few turns, and they did nothing.
Later, I loaded the save before the war started and called the space monster again when war was declared. I then used the fowtrans command in the console to watch. They aggressively attacked each other for two turns, then went to sleep. After 17 turns, the space monster woke up and attacked the Measured ships. The Measured promptly destroyed it. I did this several more times and got results ranging from destruction of the space monster in one turn to nothing for 38 turns.
The save is available here with instructions on how to reproduce this if anyone wants to try it.
Finally, this is something I’ve seen in the current 3.96 version of the game and in the 4.0 opt-in. At times, a class 5 planet will just appear somewhere. I usually only notice it when it is near something of mine. It looks like one of the AI is using the artifact called Kiln of Worlds to turn a dead world into in class 5 world. It works, but the new planet is usually in some odd location, such as this one in my area of influence and well away from any of the AI.
If the AI are deliberately using the Kiln of Worlds on these planets, why are they choosing planets in some isolated place instead of where they can actually colonize them easily and quickly? Or does this mean that something is bugged and the planet chosen by the AI isn’t being converted, but a random distant one is?