The log file that can be opened with the ‘Open logs errors’ link on the page of the module page if a module build failed does not contain any error messages. In my case it only contains some generic text about the shell script, but no information usable for debugging. Maybe error logging to that file is accidentally disabled?
if your module does not output any other logging information above standard error messages from the compiler or similar, you won’t see any additional details.
Ideally you include logging output to the comand line from within your program or script. These outputs to the commandline are collected by the workflow engine and presented in the individual module logs.
In addition you can also generate you own more extensive log files and output them along the results.
Hope this helps