Glad to hear some interesting issues like this 🙂
So you need to do few more things.
1/ verify which counter is pegging … is it CESSTIMASS ? or is it the SDCCH blocking (CCONGS I believe) ?
2/ verify the SDCCH traffic (erlang) during those hours. Is it higher than usual ?
3/ what is the SDCCH MHT ? (mean holding time)
4/ now it’s interesting to know what’s happening BEFORE the sdcch establishment. That’s called the RACH phase. In E/// several counters are available to know what is the kind of Random Access that’s occuring (i’ll let you find the related counters). Another counter is counting ALL of the random accesses. So by substracting the RA causes to the total RA, you can find the “ghost” RA.
From there I think you’ll get a clear picture of what’s occuring. I hope so 🙂
Last step is to do a RACH trace on the BTS itself, but it involves advanded tracing techniques that i havent done in years, and which are reserved for E/// personnel (afaik).
Let me know how it goes !