Hi, since plantuml.8011.jar, a "while" in each branch of a "fork" generate an empty file.
this simple example produce the failure :
@startuml
start
fork
while(condition?) is (true)
:task;
endwhile (false)
fork again
while(condition?) is (true)
:task;
endwhile (false)
end fork
stop
@enduml
It works with plantuml.8010.jar or if there is a "while-loop" in only one branch.