Hi,
For debugging purpose, you may start your simulation locally with Gatling Open Source and enable logs as you want in the logback.xml.
On the other hand, in Gatling Enterprise (FrontLine is the former name), we disable simulation logs for performance reason. Indeed, when running simulation at high scale, writing all logs on disk is a performance killer.
We do have a feature ticket about launching a simulation with logs enabled with a restricted amount of virtual users, but this is something that is still work in progress and there is no ETA at the moment.
Cheers!