wi fi – WiFi sometimes only uploads but does not download

No matter in which network I am, at seemingly random times my WiFi connection cannot download anything but the upload arrow of the WiFi icon is constantly active. So I guess, uploading should work but I have never uploaded anything when this happened, so who knows.

Reconnecting sometimes helps at the first try but sometimes it takes 3 reconnects or even more (time) to work again. Mobile Internet is fine.