If it only happens at boot, it's just a minor annoyance / glitch that I have seen on various builds of CM on other devices. You can try to clear the cache / data of the phone app in Settings / Applications / All and see if that helps. Can also try clearing cache and dalvik cache in recovery and fixing permissions. That or wait till there is a more stable version of CM for your phone and update.
Gallery issue - same thing - clear the cache and data stuff in the Application section of Settings. This could be due to not using the best set of Gapps for your setup as well.
For random reboots, that can be kernel related. I'd double check the thread for CM to see if there are suggestions for another kernel or fix for that.
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