Running N agents in parallel creates serialism at the human level, not parallelism. You're one brain, and each context switch costs 15-25 minutes of re-entry. Three agents in parallel means your effective output is roughly one agent's worth, minus the switch tax.

The flow came back for me when I dropped to a single agent with tight feedback. The subtle bugs you're describing are the direct cost of reviewing code you weren't fully in the context of when it was written. Parallelism hid the review from you, but didn't eliminate it.