When a featurefails (such as a round) you are in the following situation:
If you select the failedreference and click on what you want to replace, Creo delete all references (see next picture)
Hence to resolve the failure you must remove the failed reference (see next picture) and select a new one by holding down the CTRL key.
This is, of course , not a replacement of the old reference (so all the children of the old missing reference continue to fail).
It would be interesting to unify the behavior of a lost reference selection to what happens in the context of a redefinition of a sweep in which, if I select from the selection pane a lostreference (ex. a trajectory) BEFORE selecting the geometry on the model, the newly selected reference substitues (replaces) the old one (see next pictures).