2010 Prius gen3 showing Check Hybrid System error despite inverter replacement

I have a 2010 Prius Gen 3, with 49k miles. The car has been driven lightly in the last 5 years. About year ago, it started showing the "Check Hybrid System" error. and then stopped working (even gas engine won't work).

I took it to the dealer last week. They diagnosed a bad inverter and a bad 12v battery. Luckily, 2010 Prius models are still under the 15 year inverter warranty, so the dealer installed a new inverter under it, and changed the 12v battery.

I picked it up yesterday and it drove fine in the city as well as the interstate. But when I started it this afternoon, I got the "Check Hybrid System" error again. The gas engine was running and I could move the car. But the triangle of death with the above message showed. I detached the 12 v battery for 5 min and then restarted the car, and the error message went away. But I'm worried that the dealers must have missed something.

So, my question to you guys: What else other than a bad inverter could have caused this? Since they replaced the inverter, there must be something else malfunctioning as well. I'm worried to take the car to the road as I don't want to get into limp mode and be stranded. Can someone help please?