Trouble USB flashing Athom WLED controller

using FTDI cable:

$ esptool.py --port /dev/ttyUSB0 write_flash 0x0  Downloads/WLED_0.14.0-b1_ESP8266.bin 
esptool.py v4.5
Serial port /dev/ttyUSB0
Connecting....
Detecting chip type... Unsupported detection protocol, switching and trying again...
Connecting...
Detecting chip type... ESP8266
Chip is ESP8285H16
Features: WiFi, Embedded Flash
Crystal is 26MHz
MAC: 4c:eb:d6:d3:47:09
Uploading stub...
Running stub...
Stub running...
Configuring flash size...
Flash will be erased from 0x00000000 to 0x000c3fff...
Compressed 802528 bytes to 573124...
Wrote 802528 bytes (573124 compressed) at 0x00000000 in 53.2 seconds (effective 120.6 kbit/s)...
File  md5: 3023a1710dd1ac297ee2143bfffdad4c
Flash md5: 9b97f71c2161b0d18c23e60f5cfd6d3a
MD5 of 0xFF is a1c5e0888399bcd536690f684c3a6517

A fatal error occurred: MD5 of file does not match data in flash!

The Flash MD5 is different on each attempt.
“Manual OTA update” from 13.0-b6 is failing. - that’s why I use an FTDI adapter. (and tried two different FTDI adapters)

EDIT:
this is crazy, but at third test with second adapter … it worked:

....
Flash will be erased from 0x00000000 to 0x000c3fff...
Compressed 802528 bytes to 573124...
Wrote 802528 bytes (573124 compressed) at 0x00000000 in 71.3 seconds (effective 90.1 kbit/s)...
Hash of data verified.

This is very odd … I had short cables, and the baudrate is not crazy (given 90kbit/s) … is this normal?