I have the Samsung Galaxy J3 for about a year. In these last day my phone fails to connect to WiFi automatically. I have to put off the modality "WiFi" on my phone, restart then the phone and put on the modality "WiFi". After this method the phone manages to connect. Someone can tell me another way to solve the problem?
I have the same problem with my samsung galaxy S4. Try to reset the phone and if the problem persists try with phone formatting. I solve this problem with the second way I told you. I hope that I can help you