When you turned the midi logging on you should have seen a warning from HW that you had indeed turned this on - you need to agree to continue with the logging. (If you did not see this message then logging was not actualy turned on.)
Rather than turning the midi loggin off before you browse the log file, browse the log file after pressing the piston configured to advance the stepper.
Make sure you browse to the bottom of the log file...
You should see an INF message which gives the midi information sent when you press the advanced piston.
When midi loging is enabled you may see other traffic generated by your console (all notes off messages from the keyboard for example) - ignore these.
What do you find in the log?
Remember to turn midi logging off when you've looked at the log.
Do you know what midi commands your pistons are supposed to send. It might want to check what HW has detected for your stepper advance.
On my console the pistons all send notes on/off messages.
You can see what HW has detected when you autodetect the piston by right clicking on the virtual control and selecting Adjust midi trigger settings. This url takes you to an image of my settings for an advance stepper piston.
http://iainstinson.com/hauptwerk/advance-piston-settings.PNG. The output, input 2 and output 2 tabs should inidicate that these are disabled. Is your similar?