Happened to me today, tried to turn my screen I pressed the home button but it didn't turn it on so I pressed it again and it still didn't turn on then after 2 secs the screen blinked.
It only happened this morning that it didn't respond twice then blinked after 2 secs after being pressed.So if it only happens first thing in the morning it is just waking up.
If it does it all the time then you got a problem.
Good to see you are using your account again.
Did you try a reset (turns off and on again) ?
Next step I would advice is a complete restore.
Last chance a visit to the Apple Store if anything else fail.
https://forums.macrumors.com/threads/battery-percentage-jump.1943650/
https://forums.macrumors.com/threads/percentage-drop-while-charging.1940506/
https://forums.macrumors.com/threads/charging-on-and-off.1940612/
https://forums.macrumors.com/threads/iphone-6-camera-rattle.1940419/
https://forums.macrumors.com/threads/can-hard-resetting-damage-my-iphone-6.1931005/
https://forums.macrumors.com/threads/charges-my-phone-at-99.1942380/