If you embed 2 times using !include of the same file, the second embed will fail
Create a simple include.iuml (title is ennough), then try:
@startuml
a<-->b
note right
{{
!include include.iuml
}}
end note
a<-->b
note right
{{
!include include.iuml
}}
end note
@enduml
If you copy include.iuml into include2.iuml, then in 2nd embed use the include2.iuml, then everything will work fine