I've tried a full erase.
This is what it says about the disc:
HL-DT-ST BD-RE GBW-H20L YG01 (ATA)
Current Profile: BD-R
Disc Information:
Status: Empty
Erasable: No
Free Sectors: 12,219,392
Free Space: 25,025,314,816 bytes
Free Time: 2715:27:17 (MM:SS:FF)
Supported Write Speeds: 2x
BD Disc Information:
Disc ID: SONY-NN3-02
Disc Type: BD-R
Performance (Write Speed):
Descriptor 1...
-> B0: 0x02, B1: 0x00, B2: 0x00, B3: 0x00
-> EL: 12219391 (0x00BA73FF)
-> RS: 11,161 KB/s (2.5x) - WS: 8,991 KB/s (2x)