This issue is fixed in the next update. It is visual only.
When upgrading your Kingdom Power Level to Power Level 5, you should receive +1 to all Skills/Stats on your Troops. However, in the Kingdom Level screen, this is only showing as one level behind. For example, it rather than showing as "+2" it will only show as "+1".
Fixing the problem
This is a visual issue only, and the skill bonus will still be applied in battles. This is fixed in the next update, 3.6.