My wife got the Nokia 6.1 (2018) and likes the phone, apart from the fact that it gets very laggy (non-responsive). I have seen the issue first hand, and pulled debug logs.. A few things I notice.. The main one is the CPU load when laggy.. The big one is very high CPU usage from kswapd0, and a bunch of other services such as 'system'.. To me, this indicates that the device is spending way too much time swapping in/out of memory / cache.. Thus blocking and causing non-responsive behavior.
Things like com.evenwell.powersaving.g3 94mb of PSS 8mb of swap..
Seems like high Memory->Swap is probably causing the issue..