launch_runs synth_1 -jobs 6

 

To work around the issue Black box :

Open the synthesized run from the Vivado IDE. The Tcl equivalent would be:
open_run synth_1 -name synth_1 -pr_config [current_pr_configuration]

Enter the following command in the Tcl console:
setup_pr_configurations -v -use_netlist -force

Close the synthesized design. This can also be done from the Tcl console:
close_design

Launch the implementation run.