nand flash 启动坏块，有了解过的吗？

海思3531a的板子 nand flash启动。
启动日志大致如下：

Check Flash Memory Controller v100 ... Found
Check Nand Flash Controller v610 ... found
Special NAND id table Version 1.38
Nand ID: 0x2C 0xDA 0x90 0x95 0x06 0x00 0x00 0x00
Block:128KB Page:2KB Chip:256MB*1 OOB:64B ECC:4bit/512
Nand total size: 256MB
*** Warning - bad CRC or NAND, using default environment
...
VFP support v0.3: implementor 41 architecture 3 part 30 variant 9 rev 4
yaffs: dev is 32505858 name is "mtdblock2" rw
yaffs: passed flags ""
VFS: Mounted root (yaffs2 filesystem) on device 31:2.
Freeing unused kernel memory: 172K (c05bf000 - c05ea000)
Welcome to HiLinux.
...
系统启动后，输入dmesg
~ # dmesg
yaffs: checking block 1692 bad
yaffs: checking block 1693 bad
yaffs: checking block 1694 bad
...
yaffs: checking block 1998 bad
yaffs: checking block 1999 bad
yaffs: yaffs_read_super: is_checkpointed 0
VFS: Mounted root (yaffs2 filesystem) on device 31:2.
Freeing unused kernel memory: 172K (c05bf000 - c05ea000)

udev[702]: starting version 164
Hisilicon Media Memory Zone Manager
...
有的时候启动只提示以下异常：
VFP support v0.3: implementor 41 architecture 3 part 30 variant 9 rev 4
yaffs: dev is 32505858 name is "mtdblock2" rw
yaffs: passed flags ""
yaffs: yaffs: Attempting MTD mount of 31.2,"mtdblock2"
yaffs: checking block 0 bad
yaffs: checking block 822 bad
yaffs: yaffs_read_super: is_checkpointed 1
VFS: Mounted root (yaffs2 filesystem) on device 31:2.
Freeing unused kernel memory: 172K (c05bf000 - c05ea000)
udev[702]: starting version 164

进入uboot，输入指令 nand bad

nand bad
Device 0 bad blocks

请问这种情况的坏块，可能是那些因素导致的？
希望了解过的指导下，万分感谢！