Stutter varies a lot. The main thing you need to know is that it's not your fault - it's not something you're doing (or not). It's stutter - it varies with context and over time. The best thing to do is to get familiar with it in order to not get surprised. You may try speech therapy to help manage it. (Also, don't worry about using a problematic term like "subconscious", since it doesn't have any impact on your stutter.)