This diagram renders fine:
@startuml
[Database]
[Runtime]-->[Worker]
[Worker]..>[Writeback]
[Writeback]..>Database
[Runtime]-->Database
[Runtime]..>Database
@enduml
But changing the first line from "[Database]" to "() Database" causes the renderer to crash. This is the most minimal example I could find: removing any line from the above sample stops the crash occuring.