Every time I press the button to turn the screen on it lags and I have to wait a second or two to turn the display on, any ideas on how to fix it or is it a software thing?
ADB or Android Debug Bridge is a command line tool that lets you run commands on your phone from a computer, for installing/unistalling apps, tweaking hidden system settings, etc...I have tried safe mode, yes, and the same issue persists, it's not every time the device is unlocked, it's only when it's left for around 2 minutes (it's almost like a deep sleep or something) and what's ADB mode?
Have you tried updating to Oreo? The only other solution I can think of is a factory resetYes it has been doing it since new