I dont like this, all my possible theories are being shot down.
Good call on immediate TCH Assignment, but currently there is no cell on which this feature is activated in the whole network. 😀
I noticed a rise in Handover Access failures aswell. Could it possibly be that during handover some kind of information is needed from different HLRs? Or maybe in party A a TCH is siezed but party B cannot respond due to timeout/congestion and the TCH on party A could be possibly cleared or dropped depending on timer values etc?