Hello K.,
FYI, I test locally with version 1.2024.8beta7 and all is good.
Here is the output of:
java -jar plantuml.jar -preproc myfile.puml
@startuml
class 0
newpage
class 1
newpage
class 2
newpage
class 3
newpage
class 4
newpage
class 5
newpage
class 6
newpage
class 7
newpage
class 8
newpage
class 9
newpage
@enduml
Regards,
Th.