im using msi laptop gt75 8rf with 8th i7 ,GTX1070 and 16gb ram
and my laptop supported up to 120fps ,but sometimes my ue4 fps up to 120fps jst for few second then start unstable between 15~30 fps around on even a similar object level.
Consider disabling GeForce experience, it did conflict with the engine in the past. Not sure if that’s still the case but sounds precisely like what you’re describing.
i tried but still the same issue