Looking at this, I think I see what's going on, although I can't yet be 100% sure -- the AI has decided you are too well entrenched, and is just going to probe and poke your defenses until you make a mistake. You defended yourself really well, so well fact that it decided to just wait in the wings (the Threat number is still really high, that's all those cross-planet attack ships just hanging around on their planets trying to probe you).
So basically what you are seeing is part of the new AI logic, which makes it much less likely to just throw its ships away on whatever defenses you create. You'll have to just try to keep expanding while also keeping an eye on your own defenses, and at some point it will find a weakness (either it will bolster its own defenses or go for one of your planets), and then you'll have a bigger problem.
When I load your first version, before the cross-planet attack, I get around 450 ships into Swomarur (upper right), and then they kill it and move back out into the galaxy, preserving themselves so there is still around 900 threat after they escape. In the second save that you provided, after the cross-planet attack, I notice that you also lost that planet. Given that there was no incoming wave there, that was part of the cross-planet attack, maybe you just missed it.
Then I also noticed the AI probing you in a few other places, but most likely it just takes a good while for it to get anywhere from Swomarur since that is so far away.
So, in summary, it looks like the AI is doing exactly what it should, which is being unpredictable and making things hard on you. It took out the one planet that it found that it could easily take, and now it's looking for another opening. It might take it a while to find one, since you're pretty entrenched, but it won't just throw itself on your bayonets if it can help it.