Hi @ionatx,
Yes, I believe to resolve ambiguity as to where log output ends up, the project log behavior changed between 14 and 15. In JMP 14, messages write to the global log unless the project log window (or an embedded log window for the script) is open in the project. In JMP 15, output always writes to the project-specific log, whether it is visible or not.
I can certainly see the value of having a free-floating log in the context of using a project, especially with a multiple monitor setup as you describe. Unfortunately, I am not aware of a way to detach the project log from the project itself, and I do not believe there is a preference for reverting to the JMP 14 behavior of writing project output to the global log when the project log is hidden. Perhaps others can suggest a workaround here, but I suggest posting your request the JMP Wish List.
@julian