Combining multiple roles

Answer:
There are always risks while combining multiple roles in single person (although, such situation is sometimes inevitable).

In your case I see following risks:
1. Dynamics of activities and approach for Major Incident (as well as all incidents) is quite different than resolving problems or implementing changes
2. People you are working with are different (knowledge, experience...)
3. Incident is trigger for problem management. So, you can see it as “controlling” of the problem management's efficiency
4. Problem management is trigger for change management. So, mentioned in #3 is valid here.
5. Problem management efficiency influences incident management, Same relation is valid for change management – problem management. So, if you have all these processes in one person…

This is the article that can he lp: “
What ITIL roles can be combined in one person?” https://advisera.com/20000academy/knowledgebase/itil-roles-can-combined-one-person/