possible malfunction

I have an old iphone 6 plus given to me by a relative. ive used it frequently for a number of years. recently I've had a problem while at random intervals the screen stops accepting input. I have both a case with a screen cover and a glass screen protector yet I highly doubt they are the source of the problem and the phone works normally for periods of time before the specified error. I dont belive anything is triggering the error as it sometimes can occur on the lock screen. Do any of you know what this error is and what i should do to fix it?

Thanks