RT-AC88U Bad eraseblock

[TBolley]

After Firmware downgrade.

Whats is mean with this ?

May 5 07:05:05 kernel: Bad eraseblock 533 at 0x0000042a0000
May 5 07:05:05 kernel: Bad eraseblock 542 at 0x0000043c0000
May 5 07:05:05 kernel: Bad eraseblock 611 at 0x000004c60000
May 5 07:05:05 kernel: Bad eraseblock 693 at 0x0000056a0000
May 5 07:05:05 kernel: Bad eraseblock 814 at 0x0000065c0000
May 5 07:05:05 kernel: Bad eraseblock 815 at 0x0000065e0000
May 5 07:05:05 kernel: Bad eraseblock 906 at 0x000007140000
May 5 07:05:05 kernel: Bad eraseblock 907 at 0x000007160000
May 5 07:05:05 kernel: Bad eraseblock 924 at 0x000007380000
May 5 07:05:05 kernel: Bad eraseblock 925 at 0x0000073a0000
May 5 07:05:05 kernel: Bad eraseblock 941 at 0x0000075a0000
May 5 07:05:05 kernel: Bad eraseblock 968 at 0x000007900000
May 5 07:05:05 kernel: Bad eraseblock 996 at 0x000007c80000
May 5 07:05:05 kernel: Bad eraseblock 997 at 0x000007ca0000