Ok, first of all did the modules boot before?
Or never booted?
Did you buy the modules separately or as part of the development kit?
What is the part number of the modules you bought? It is 55XXXXX-XX number on the sticker,
Do you have development board and are you testing modules on it?
Do you have a module that still boots so you know your development board is good.?
Is your Development board set to little endian (switch S4-1)?
do you have a JTAG debugger?
Is your serial port set to 115200?
Do the modules boot if you switch the board to big endian and set serial port to 38400?
Modules Digi shipps always come with at least a bootloader, however those modules come in 2 flavors - digi embedded linux (little endian) and Netos (big endian)
Once I know the answers I should be able make further suggestions.
you can also open a support case with request to investigate the issue online support request