@JRE I forget that not everyone works with 3-phase mains daily. Here I can't isolate the mains, so have to live with the concept that 'scope chassis can be "hot". "Electrician's Left-Hand-Rule," as well as "Never touch scope chassis while energized."
By all means, isolate the D.U.T. before isolating the 'scope if you can. In the former, scope chassis is always ground, so will never deliver a shock when touched.
