The second file below will result in a "</w> Syntax Error" as shown at https://pasteboard.co/IatVBso8.png. This has been a problem since 2018.11. The files render correctly with 2018.9. The problem seems to be the comment line in the first file. Removing it causes the second file to render correctly.
Thanks!
dave
includeSubIssueInclude.puml
@startuml
!startsub MAIN
' Comment
rectangle z
!endsub MAIN
rectangle test
@endum
@startuml
!includesub includeSubIssueInclude.puml!MAIN
rectangle x
@enduml