Ok, so I was wrong, sort of.
I am using GetResources to call this Chunk, in two different places on the page. The calls looks like
[[!getResources? &tpl=`module_tabs` &includeTVs=`1` &processTVs=`1` &resources=`43` &includeContent=`1` &showUnpublished=`1` &showHidden`1`]]
[[!getResources? &tpl=`module_tabs` &includeTVs=`1` &processTVs=`1` &resources=`44` &includeContent=`1` &showUnpublished=`1` &showHidden`1`]]
Inside "module_tabs" is where [[RandomNumber]] is called.
Each time it’s called, it gives back the same number. So it’s not actually two [[RandomNumber]]’s inside one Chunk, it’s two Chunks with one [[RandomNumber]] inside that is giving back the same result.
Hope that makes sense.
[Yes I understand it may be strange to have two GetResources calls like this, but it’s the only way I can achieve what I need.