An unstable internet connection is the most prevalent cause of lag. To avoid this, simply try switching to another network: If you are connected to wifi, try using your device data and vice-versa. If you can only connect using wifi, ensure that your wifi connection is 3 bars or green.
Opened apps may also use data thus we advise you to close all apps before playing Black Clover M or restart of your device.
Downloads usually hide in the background and ensure that you have no active downloads.