To have smooth playing experience
You need to be connected to fast and stable network.
WiFi antenna indicates the connection between your device and router
Therefore, it is not indicative of strength of internet connection.
Moreover, even when you connect via cellular data, there could be temporary disconnect 
It does not guarantee consistently smooth connection.
Local network could sometimes slow down which happens more often when you are in moving transport,
Especially subway.

When you play Black Survival, try to play it in area with stable network connection!