I don't feel like I stutter more on vowels, in fact I think I stutter less on vowels, except for TWO exceptions : - The "Au revoir"s (I'm French): sometimes I put so much pressure on myself to say it fluently that I don't even have a block but just a straight up mouth paralysis. No tension or anything, just unable to open my mouth and activate my vocal cords, zero muscle activation. - I have a problem with words or phrases beginning with a y, because the resulting block always forms a kinda ugly "j". English example : "yyyy-j-j-j-jou are" instead of "you are". An actual example : Yy-j-j-j-johan instead of Yohan (my middle and preferes name)