Damn, this is pretty much the exact same as me , I thought I was the only one who had a variation like this. I used to have an awful stutter and as I grew older it slowly went away. But letters starting with vowels when I have to begin a sentence with them I usually have a block on, but once I’m past the first word I speak really coherently and you wouldn’t think I have a stutter at all… The worst is when someone’s name begins with a vowel and I try and call them by their name and can’t say it but don’t even try to say it to avoid the embarrassment of stuttering sometimes. But if someone asks me a question like in an interview setting again you wouldn’t think I stutter at all. It’s frustrating but overtime it should get better for us. I do think it’s a nerves thing for me sometimes cause in some cases I can say these words, but my brain pre-emptively knows they are words I have struggled with in the past so it creates a block maybe?