Hi, this has happened to me a couple of times in the past week. Both times, my phone was in sleep mode and when I tried to use it again, it was totally dead. I could not turn it on or do anything until I took out the battery and reinserted it. then it boots up like normal.
I did the update, and both times it happened after the update.
Occasionally the phone randomly reboots when I am browsing online but this is different.
By the way, as has been mentioned in the other thread, long-pressing the power button (for me about 20 seconds) has helped most (if not all) people in that they don’t need to take out the battery to start the phone when it is in the frozen state.