Can't Extract system.img from H815T-HK

After updating H815T-HKG to v10c through LG Bridge

It can't use this command to extract the system.img

Code:

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dd if=/dev/block/mmcblk0 bs=8192 skip=55296 count=529920 of=/data/media/0/system.img

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After a while, the folder has nothing changed,

so is it the number of block is changed?

BTW, can't download the kdz through LG kdz checking website

so can't extract the kdz to fix it. :(