They are probably talking about the Matrix.org instance being slow at fetching messages for you, additionally to the delay needed to get keys for them in encryp

They are probably talking about the Matrix.org instance being slow at fetching messages for you, additionally to the delay needed to get keys for them in encrypted rooms. This is far nicer on smaller home servers, but matrix.org is the "default experience" of element and that's what people are judging it by.