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It looks like 4-5Mbps on 4G is a new standard in Vodafone and there is nothing wrong with that according to customer support because this is caused by high demand (why this is happening to Vodafone only, they didn't tell). They asked me to reset my network settings to default and when I said it has nothing to do with my mobile as I have the same issue with another mobile in Vodafone they decided to reset network settings on network side. Unfortunately that didn't change anything. I also have Giffgaff SIM in my household and as you can imagine it won't drop below 25Mbps on the same mobile. 5Mbps wouldn't be that bad if it wasn't followed by random timeouts on page loading. Dear Vodafone, is it a time to change network operator?