I have an s10+ and the wifi speed is weirdly slow. Searching or loading in apps take a lot of time, for example searching something or youtube, loading posts on reddit, entering to a web page in Google, etc, sometimes its so bad that I have to use 4g which is faster. However I can still watch 4k videos without interruption and downloading large files in seconds, and in speedtests like ookla and fast I get 250-400 mbps even though those take several seconds to start up. This only happens on my phone since October, in my laptop and other devices everything loads quickly.
I have tried resetting network settings and switching between 2.4 and 5ghz but it didn't work.