Im using m30s too and s secure is worki g fine for me. Whats is hidden even from searches. Did you 'Mask' whatsapp or just locked it? Mask is for hiding apps and lock is for locking apps which will show up in home screen.
I read somewhere that galaxy M series had been developed based on other software platform and device concept compared existing Galaxy devices. So, some applications/features are not supported and some are changed to downloadable concept on Galaxy M series device.
