There seems to be a miscalculation when it comes to worker-requirements.
At some point the AI started to constantly use more workers than it can afford mineral-wise.
This has been constantly happening and got worse once they got Tier 2 Factories and the +25% Industry-Advancement.
This means a lot of potential science is wasted since the workers cannot produce without minerals.
Food production on the other hand is totally perfect all the time. They adjust it every turn to stay between 0 and 10 foodstockpile.