I had that issue with my ESPN app - try resetting (unplug router for 30 seconds) then turn back on. Also, re-boot phone. Mine worked after that. Good luck!
Hello Welcome to the Community. Having certain apps not work with Wi-Fi stably can be a frustrating experience. It is possible that the app(s) themselves need cleaning. You can follow this guide here to rule that out: https://www.samsung.com/us/support/answer/ANS00077611/
If the behavior is still present, and the Wi-Fi instability occurs with pre-installed apps as well, you can try Safe Mode to see if another third-party app may be responsible. You can test this with Safe Mode: https://www.samsung.com/us/support/answer/ANS00062983/
You can also try to reset the settings. Settings>General Management>Reset>Reset all settings If the conditions continue under Safe Mode, or it only affects third-party non-pre-installed applications, it may be time to try a factory reset. Back up everything you wish not to lose prior, and follow the guide carefully: https://www.samsung.com/us/support/answer/ANS00062029/ If the troubleshooting is not helpful, the phone will need to be evaluated by a certified technician.
You can use the following link to find a list of service centers in he U.S. that can do the repair: http://www.samsung.com/us/support/service/ or by contacting customer support at 1-800-726-7864.
