Actually, I'm thinking sites that should be added but are being prevented by their disputed status.
I am not sure that South Georgia would be on this list anyway. For a site to actually be "prevented" from being inscribed by UNESCO it would have to be a very clear case of a State Party (SP) nominating a site over which it didn't have de facto control - e.g Argentina nominating South Georgia !!!!
UNESCO makes it very clear that inscription should not be read to mean acceptance of frontiers - but it does mean an SP taking responsibility! (but see below)
In its T List review of 2011 UK does actually mention that IUCN had suggested the nomination of South Georgia. See - https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment _data/file/78234/Review-WH-Tentative-List-Report_March2011.pdf
See paras 4.5 and 6.9 - the latter states "Potentially there is more scope for natural inscriptions from the Overseas Territories. Indeed two of the specific site proposals from the IUCN Gaps Study are British Overseas Territories (South Georgia and Chagos Atoll) though neither has been proposed for this Tentative List.
I get no sense that the failure to include South Georgia in the T List had anything whatsoever to do with the "territorial dispute". At the time UK was involved in a very long term "clean up" of the whaling stations on the island getting rid of asbestos etc. When we were last there in 2007 quite large areas of Grytviken were closed off because of this. I am pretty sure that UK would nominate if it wanted to - knowing that IUCN would support it!
The Preah Vihear inscription was a good example of where UNESCO just wouldn't involve itself in the contending claims of Thailand/Cambodia.
The Palestinian nominations are perhaps a "special" case because of the inbuilt pro-arab majority on the WHC but Hebron got inscribed even though it isn't even under de facto Palestinian control!!!
Perhaps an example of what you are looking for is the multiple failure of the "Triple Arch Gete of Dan" which seems to have been repeatedly rejected (despite ICOMOS concluding that it possesses OUV) because the UN wouldn't provide a map which showed that the buffer zone was inside Israel (at least that is what I understand to be the excuse - Assif and I have discussed it and he may be able to be more precise.