It seems TTreeCache is not properly caching, starting version 5.34.11.
I noted it when testing ATLAS D3PD analysis scripts. I can reproduce it with simple TTree:Draw example, see attached output of TTree::PrintCacheStats(); for 5.34.11 and 5.34.10 when executing attached script.
In case of TSelector type analysis 'Cache Efficiency Rel' is basically 0.
Problem seems still present in higher version, e.g. 5.34.14