I was experimenting with VFIO VGA passthrough into a Windows VM from Linux. One recommendation on the developer’s blog  was to check the rom file for an EFI rom. He wrote a parser, that checks that . So my first card eventually died, but I still have its rom file, so I could compare it to the new one. For the first one the parser could correctly find an EFI rom, for the replacement card not. The parser unexpectedly reaches the end of the file.
Both cards share the same Atombios version, but the size differs. The first one has 116 blocks (1024 bit), the new one just 60 blocks. I would attach the two Bios roms, but that might violate the forum rules. I can PM them to a moderator though.
The card is a Sapphire RX480, 8Gb, reference design.
Atombios version: 015.050.000.000.006785