Your influence has not decreased. Your influence relative to the rest of your region has decreased. For example, if there are 10 other nations in your region, you have 100 influence, and the rest have 10, then you have half the influence in your region. But sometime in the future, you may have 1100 while they have 1010; now you barely have over 10% of the total. Thus, over time, everybody's relative influence will tend to level out, so it will appear that you've lost influence. Deceased nations keep their influence, so when they're revived, as you say on your RMB that several have been recently, this can have a significant effect on your influence relative to the rest of the region.