2012 Hyundai Elantra ECU fault

Car: 2012 Hyundai Elantra

I drove 5 hours round trip last weekend without any issues. The next day my neighbor mentioned some lights flashing on my car over night.

The battery was completely dead.

I tried twice to jump the car (carefully following the safe procedure). Nothing.

I brought it to Autozone for a charge and test since it's from 2018.

Battery came back good and charged without issue. My car started up no problem and I left it sitting and checked on it again the next day. Still starts up fine.

Today I went to start it via my remote start and the engine would start very rough and die immediately.

My OBD2 read off a C1700 code or faulty ECU.

From what I've read issues are rarely a faulty ECU.

Any ideas what is going on?