This is a known limitation. If you use HW timer for getting the timestamps, you can't use Scope/Display to visualize signals.
Scopes/Displays only work with Simulation timestamps only.
Only SDI(Simulink Data Inspector) Dashboard Scope/Dashboard Displays can be used for visualization when HW timer for getting the timestamps is enabled.
You can enable/disable the "HW timer for getting the timestamps" here:
check box available in 'Configuration parameters > Hardware Implementation > External mode > Use actual timer to log realtime stamps' - with this option enabled, Scope, display, from workspace, to workspace blocks will not work as already noted above.