I'm having exactly the same problem but only since I switched ISP provider to Virgin Media, but only on the Galaxy J5 phone, I have better Samsung phone for work and it is fine. The J5 wifi keeps disconnecting and returns random errors each time, like Authentication error occurred, etc. then I click again, it connects, so the Authentication error was a joke and then it disconnects again and back to square one. Any ideas, or should I switch to an iphone? Nobody from Samsung seems to have a clue here.
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