Recently, I realized that a lot of new log files were being generated in my Commerce Minions instance. Upon further inspection, I noticed that they were being generated at 20 min intervals.
I immediately realized that the IIS application pool must be resetting. I went over the application pool settings and found that the default Idle Time-out was set to 20 mins:
This is just the default setting when a new application pool is created in IIS. You can set this to 0 to make sure the application pool is is not terminated. Also, while you are in there make sure that the Start Mode is set to AlwaysRunning.
P.S. In case you have the totally opposite problem, i.e. no logs files are begin created at all in the Commerce Engine, have a look here.