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I feel that many of these are just Android flaws so we're safe thanks to MIUI. I would also recommend checking that it's your modem before any forgetting of saved passwords or rebooting your phone. Chances are your wifi signal will be the issue long before any devices receiving that signal for example here in America our internet connection drops at a moment's notice. I've suffered many days where out of nowhere I'll lose my broadband for a few minutes. So check the modem first.
From what I've noticed if the internet is doing fine then it is either the wifi toggle that's doing it or you just haven't rebooted in a while so do that. So that's how I'd prioritize before going into any of the other steps. Wifi toggle, modem, reboot.