I use the jetbains plantuml plugin
Works great to have many diagrams on the same generated image.
Each diagram is separated from the previous with a "newpage" tag
However plantuml seems to assume all the diagrams to be of the same kind.
example it works if all diagrams are usecase diagrams.
it doesnt render the right way if example a usecase diagram follows a state diagram
A way to fix that would be to be able to specify the type of diagram to render on a specific page
title "my usecase"
(blabla) -- (blabla2)
newpage state_diagram <--------- specify the type of diagram to render
title "my state diagram"
[*] -- state1