I just had a system wakelock for the past 4 days or so. At first, I thought it was the kernel that I was using that caused it, so I flashed back to the previous version, but the same issue was happening. So, last night, I wiped data and setup my phone again, restoring minimal data from backup. After 8 hours, the phone hasn't had a serious wakelock and idle battery drain is back to normal.