Perhaps you have a random flip somewhere. Or you're calculating the CRC32 for 0x4-0x10000, when I really meant 0x4-0xFFFF. Or you've done it all correctly and are looking at the checksum with the wrong endian-ness. Or BBT has shifted the data. Or you've accidentally pulled the OOB data into your dump as well. So many options.
I also hope you verified your CH341A is actually outputting 3.3v instead of 5v over the logic lines as well, otherwise you will be pushing the SPI-NAND out of specified limits. Mine required some minor modifications to the programmer board to output the correct voltage.
There'll be much easier install instructions in the future.