the location updates takes 10s because it is “rejected” I guess. The core network does not answer to the LU REQ, so the MS is waiting 10s then it “drops” the sdcch.
That’s a possible scenario, I’m not saying that’s the answer 🙂 But it sounds reasonnable. In your case, the problem would come from VLR/HLR rather than the MS.
MS repeats the LU REQ because the previous ones didn’t get through.
If you are lucky enough to trace your situation, let me know !!