Google Nexus 4 — Freezes when idle

First time here...I have Google Nexus 4 that all of a sudden will lock up on its own when idle. Only way I have found to restart is to hold the power switch for about 30-45 seconds, then press it again until it restarts. Note, this will freeze even when the notice light is blinking. Quick discussion with repair service said the only thing they can think it might be is a glitch with 5.0.1 update. This only seems to be happening since it was updated, but not positive that is the cause. I have done a factory reset but still occurs. This may freeze often (did 3-4 times this morning) and then may not freeze for awhile (hasn't does it since...and might go day or two without freezing). This only occurs when the phone is idle...never when in use - at least so far. Could this be a glitch with 5.0.1, or is there another cause? Ideas, suggestions? Thanks, Bill