First of all, CAPA's need continuous monitoring of the progress to pervent them going into a damaged stage.
If a CAPA went into a damaged stage, then the first thing to investigate is, as Raffy said, the management support and commitment. The managament responsible for the area of the CAPA needs to define a revised action plan that is realistic based on available resources and the priorities based on the associated risk. If management is not held responsible for the plan, there will be no commitment nor support. Even if a plan is defined by the CAPA owner, appropiate management needs to approve so they can be held responsible for adherance to the plan and the required resources to do so. Likewise, management is responsible for the CAPA owner's commitment in adhering to the revised plan.
Commonly the QA department monitors the CAPA process to assure CAPA action items do not go overdue. Progress reports are provided to senior management.