I recently came across an official article by the Israel National Park Authority which explains the postponing of the nomination as follows:

The committee feared Arab members would impede the nomination and create a precedence of political interference in the nomination process.

It is weird this appears in an official Israeli website of a national authority whereas all Unesco sources supply different explanations involving conservation issues.

Is there any particular "Reason" (whether rational/logical or not) why the Triple Arch Gate should be more likely to incur this political opposition from Arab States than other Israeli sites which have managed to get inscribed in recent years (Incense Route - 05, Biblical Tells - 05 and Bahai Holy Places - 08)?

And do we know what words/explanations were/have been used? I note that within the draft decision paper
http://unesdoc.unesco.org/images/0018/001881/188131e.pdf
the recommendation has been hidden away in an appendix which, as far as I am aware we don't have access to in the version obtained by Durian - WHC-10/34.COM/8B.Add

The ICOMOS review seems perfectly positive
"ICOMOS considers that the changes made since the property was first nominated for the World Heritage List in 2005, and since the 2008 evaluation, have been positive, particularly with regard to the enlargement of the buffer zone and the marked improvements in property conservation work and in the monitoring of the property.
Recommendations with respect to inscription
ICOMOS recommends that the Triple-arch Gate at Dan, Israel, should be inscribed on the World Heritage List on the basis of criterion (ii)."
And also reports very candidly how Israel had satisfactorily supplied the information requested at the 32nd and 33rd WHCs! I see also that it was withdrawn before the 30th session in 2005 - when of course Israel got 2 other inscriptions.

Probably because of its location, right at the border of the disputed Golan Heights?

Yes, I am aware of its location - and also of its "cultural significance" in defining the extent of Biblical Israel as in "...Dan to Beersheba" (the other half of which got inscribed in 2005!). As far as I am aware it was recognised as part of Palestine in the days of the British mandate and became Israeli in the war of 1948 - hence its legitimacy as part of Israel would seem no less than that of other parts which were so assigned by UN and which include inscribed sites. The "general view" (not necessarily accepted by Palestinians or Arab states of course) is that any future settlement should be based around those boundaries which would not include Dan as a part of a Palestinian homeland in any 2 State solution.
We know that any attempt by Israel to gain inscription for any lands acquired in the 6 Day war (other of course than the "special case" of the Old City of Jerusalem) will not be entertained by UNESCO let alone the WHC but this doesn't seem to fail on those grounds.
So is it purely the psychological/cultural "red rag" of the claim that Israel went that far north which "upsets" Arabs or are there special historic events around its inclusion in the original part of Israel? No doubt Assif will know!

My speculation in this regard are as good as anyone else´s. Maybe Arab policy towards Israeli nominations as a whole has changed. Importantly, both Bahai sites and the Incense Route have no connection to the Zionist narrative and even the Biblical tels´connection to the Zionism isn´t that obvious. The triple arch of Dan is the location of the famous David stele with a reference to King David in Hebrew. Of course this is something different.