Just a reminder: when you enable a reference, if it is to a VIEW (View Map), the process will be slower because potentially different layer combo, model view options, etc etc are rendered for both the active and the trace. For complex models or for slower computers, this can be noticeable.
If the reference is to a viewpoint (Project Map), then the exact same layers, model view options, dimension settings, etc etc are used for BOTH the trace AND the reference and things are much faster.
(For old-timers who remember Ghost Stories as the only 'trace' option ... with the old Casper-the-Ghost button ... this latter type of tracing to viewpoints corresponds exactly to the old ghost story.)
See if tracing a View vs Viewpoint might explain the slow behavior you are seeing?
See further info here:
http://www.archicadwiki.com/2dSpeed?highlight=%28CategoryTrace%29#Trace_and_Reference
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