I can reformat that example text for you, in case it speeds anyone else up helping you.
top to bottom direction
A -- AChildLeft
A -- AChildRight
note as AChildLeftNote
AChildLeft -left- AChildLeftNote
note as AChildRightNote
AChildRight -right- AChildRightNote
As you would expect, the online server renders correctly:
To be fair your problem is more with RHEL support of Graphviz, than with Plantuml - it is putting RHEL to shame compared to other unix brands - hopefully you are also trying to lobby in that direction too. I don't know if Plantuml have any appetite to try to work around bugs/differences in such an old version. Have you tried going back even older with Graphviz (eg 2.22) in case it was an issue introduced in 2.30?
I think your best bet is with 'project Smetana' - Plantuml's attempt to rewrite Graphviz in Java. Adding "!pragma layout smetana" to your example gives an accurate diagram, although it chooses a different order for the two child components (I'm not sure if this is a bug or an expected limitation of conversion).
So maybe a better way forward is to use Smetana and file any bug reports to help improve it. (I'm not sure if it is still being worked on or is considered complete.)