2006 Toyota Sienna P0328 Knock Sensor Bank 1 - Diagnosis and Solutions

I've been experiencing a persistent P0328 Knock Sensor Bank 1 error for approximately six months. The issue consistently appears at the same two gas stations I regularly use, though I've tested other stations as well. When I clear the code and add STP Bently Legal Octane Boost with fuel injector cleaner, then refill the tank from a completely empty state (17.525 gallons), the P0328 code disappears and remains absent for several days. However, after about a week of driving without additives, the knock sensor error returns. I can clear it manually, but within just one start cycle, the code reappears. During use of the octane booster, I do not experience any engine pinging or knocking, and no other misfire codes are present. My spark plugs have been replaced recently, and there are no miss counts or related fault codes. This suggests that the knock sensor itself or its wiring may be functioning properly. I suspect a potential fuel injector issue on Bank 1, but I'm not certain. The freeze frame data shows unusually high airflow at 15 g/s with throttle position at 16%, RPM at 765, and speed at 0 — indicating a possible abnormal condition during idle or light load. When using the octane booster, MAF readings drop to normal levels (approximately 3.3 g/s, fluctuating between 3.1–3.5 g/s), which aligns with expected engine behavior. I recently had my timing belt replaced and have since changed spark plugs. What are the most likely causes I should investigate next? Is it possible that a fuel injector on Bank 1 is causing inconsistent combustion or misfires that the knock sensor detects indirectly?