No changes have been made to the AI for a few months now so I don't think it's a change in that regard.
Which map and which mod are you using. Have you tried it without said mod? Usually a 5.9 AIX should result in pretty quick teching and building.
One thing you could do is observe the AI to see what it's doing thats causing this problem. There are also logs produced that can give us an indication of something is going wrong that's stopping it