The game feels completely broken at slower game speeds, I would suspect this is the cause of the problem.
The time factors have a lot of dodgy things going on effecting game balance, I was able to capture 2 nodes with an engineer that I had built from the seed before the creeps began to spawn. It isn't just the node capture time though, regen rates, combat, it all seems out of whack when playing on Slower speed settings.
Playing against Beginner AI on Slower, the AI stayed at 28 until around the 30 minute mark, dropped to 4, then at the 45 minute mark I put it out of its misery, it had done nothing.
Playing against Normal AI on Slower, the AI took about 20 minutes to exceed the 54 score bottleneck (this score would represent 2 engineers, building a base, not building an army). After about 40 minutes it had crawled its way up to a score of 400, and had captured 4 nodes around the seed although the AI was easily wiped out.
Edit: Two comparison clips below demonstrating the relative difference in game speed.
Normal Speed - 2 Nodes captured before creeps spawn:
Slower Speed - 5 Nodes easily captured before creeps spawn: