Are you using a quick circle case by chance? I noticed serious lag while using the circle case. I thought it was xposed, mod themes, etc. I uninstalled, went to stock and have the same issues. I noticed it the most when opening the flap and had the setting to unlock the phone when opening the lid. I shut off quick circle app and it all went away just like that. Massively disappointing and am not sure if it is my case or the app. Can't imagine it would be the case, but will have to find buy a new case to troubleshoot more. Im using an Lg G3 qi/nfc quick circle case.