2013 Toyota Aqua EGR Nightmare — Fixed the Code, Now Horrible Fuel Economy. Advice Needed!

I’ve got a 2013 Toyota Aqua and a few months ago it threw a P0401 fault code (EGR insufficient flow). My local mechanic cleaned the EGR, and the check engine light went away — but it came back after about 30-40 km. He cleaned it again, same story.

Took it to a few other mechanics, and they all recommended replacing the EGR. Reluctantly, I bought a new one, got it installed… and a few days later, the same code came back. The mechanic replaced it under warranty and then sent me to an electrician who updated the EGR software/ECU settings. That finally stopped the check engine light.

Now the problem is terrible fuel economy.
Before this whole issue, I was consistently getting around 20-25 km/l (450-550 km per tank). Now it’s barely hitting 12-15 km/l (around 350 km per tank). I didn’t notice at first, but it’s been a month and it’s consistently bad. I even tried different petrol stations thinking maybe it was fuel quality, but no luck.

Anyone know what might be causing this after an EGR software update and replacement? Could the update have messed with the ECU settings or fuel trim? Or should I be looking at something else now?

Would appreciate any advice!