Is the S6 more sensitive to wifi strength? My S6 is constantly shutting off wifi and turning itself back on, so I am thinking it could be wifi strength, or is it a setting? My S3 never had a issue with this.
I'm thinking it is a setting. Go under the wifi settings and you should see some options. The only one I always turn off is allowing wifi to scan for networks when wifi is turned off. But, I think on previous phones there was Smart Network Search or something like that.
In your wifi settings, tap the menu and go to "Advanced" make sure Wifi Sleep Policy (or similar) is set to Never.
Also, does this only seem to happen at one place? ie, just at home? It may be necessary to power cycle your router. I know that's fixed it for me before on my Note 4. Turned out it wasn't the phone, but the router. Though, the Note 4 still seems to popup the message that it's connected to my network randomly even though it should've been connected all along.