That happens, usually you have to clear the reply box out and start again, sometimes it will give you the option to continue with the reply or clear the editor and start again. Trying to highlight a portion to quote can be tricky sometimes and sometimes it will go up, or down, very quickly to highlight the whole text, am on an iPhone, difficult to separate the red dots if they are close together. Sometimes easier to hit select then reduce the highlighted text down to what you want. I find the “ quote “ button is in a better place now than before, maybe it was close to the emojis before ? Used to be in a black box but now is in blue text and I haven’t hit it for ages so am pretty sure it is better for me, at least. Could be in a different place on your phone or pc i guess.