Did you just get it or have you been using it for a few days already?
Doubtful, setting it up as a new device is usually the best way to make sure you don’t get any corruption. I’d use it for a few days and see if it gets better. iOS 11.4.1 isn’t exactly perfect so you might have to wait for iOS 12 for performance improvements. Was your iPhone 8 stutter free?Got it yasterday.
It’s refurbished
I didn’t restore it, only “delete all settings and content”
Is this might be the resone?
Doubtful, setting it up as a new device is usually the best way to make sure you don’t get any corruption. I’d use it for a few days and see if it gets better. iOS 11.4.1 isn’t exactly perfect so you might have to wait for iOS 12 for performance improvements. Was your iPhone 8 stutter free?