There seem to be many issues with slow WiFi on Samsung devices specifically for apps and no good solutions. I'm on a Samsung Note5 and apps like Facebook or Instagram won't load on my home WiFi. I know it's not the home network because other devices work fine. Also to narrow it down to possible problems I tried just connecting to WiFi in airplane mode. When in airplane mode the apps load up quickly without issue on the same WiFi connection. Switch airplane mode off and WiFi issues come back. Also when disabling just mobile data the WiFi is still slow. It seems to be an issue with WiFi and voice networks on at the same time.
Does anyone know if this is a known problem? Problem with Sim card? Solutions?