The results image is of a seed ROI-based correlation with the rest of the brain WITHIN one condition’s betaseries estimates (strong beat). I get equally widespread correlations for our other ROI seeds as well.
You seem to assume that the brain should not be highly synchronized among most regions under a task/condition. Is it possible that your results are showing something closer to the reality rather than an abnormality? Most of the time people focus on the differential effect or contrast between two conditions/groups, which are usually much more subtle and less dramatic.