For me, the stutter gets worse when i am nervous which i think is pretty universal for stutters. and in the case of a visa interview, it makes total sense why you are struggling more than usual! For serious situations like this, my recommendation is to start the conversation up front by saying you have a stutter so no one is surprised. Instead of wondering why you are so nervous bc of the stutter, they’ll already know you have it. Does it always work out this way? I’ve done this for job interviews and i havent gotten all of them, but it makes the experience easier on me and probably on the interviewer when i disclose. Good luck, you got this