Wi-Fi No Internet Issue

I have bought my Xperia Z3+ Dual about a year ago, and since I started using it, I had problems with Wi-Fi. The Wi-Fi works fine but randomly stops recieving data and then I get an no internet exclamation point near the icon, but the Wi-Fi is connected and sending data, I can see on the icon, to get Wi-Fi working again, I need to restart Wi-Fi on my phone. I have tried resetting my phone to factory settings, but it didn't help. My sister has the same phone and she has the same issue. We both experience it especially when using Instagram. I only saw this issue on Xperia Z3+ Dual phone. I would like if somebody could recommend me an solution to this problem.

Please help.
Thanks!

I didn't find the right solution from the Internet.

References [url]https://talk.sonymobile.com/t5/Xperia-Z3/Wi-Fi-No-Internet-Issue/td-p/1251767[/url]

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