AMG GT Hybrid Radio Reception Problems

That's no fun! Radio issues in a modern car are often trickier than they seem. A defective antenna is definitely a suspect given the error code. Antenna boosters and signal amplifiers can sometimes go bad, causing radio interference and poor signal, and the antenna ground needs checking. Before tearing things apart, have you checked the basics like the antenna connection itself? Sometimes they can loosen or corrode. Also, any recent work done on the car that might have disturbed the antenna wiring? Corroded antenna ground can cause that as well.

I did a quick visual check of the antenna connection, but didn't see anything obvious. When you say antenna ground, do you mean where the antenna physically mounts to the car's body? Is there a specific way to properly test that connection, using a multimeter or something?

Precisely! The antenna ground is where the antenna base connects to the car's body. Ideally, you'd want near-zero resistance between the antenna base and a known good ground point on the car's chassis. Now, while you could chase that down with a multimeter, given the cost and complexity involved, and the fact that you're already seeing error messages pointing to antenna issues, I think it's time to consult a professional. These systems can be sensitive, and sometimes it’s faster and cheaper to go to the shop.

Took the car to the workshop. Turns out the antenna was defective. The repair bill came to about 255€. Everything is working fine now.