The bootloader on the Creality Ender 3 “silent” boards (v4.2.2 and v4.2.7) has a weird quirk: it will only flash if the firmware file has a different name than the last firmware file used to flash the board.
Currently, the “flash-sdcard” script simply uploads to “firmware.bin”, which works exactly once before failing with a “version mismatch” error on subsequent updates.
This could theoretically be fixed by adding a unique timestamp or version string to the filename.