I'm not sure how normal this is, but I think almost exclusively in abstract representations of concepts in my head and rarely ever use words.
This means while I often feel I have a good understanding of something and everything makes sense in my mind when I go to explain something I then realise I don't know what things are called or how to describe what's in my head.
The issue is mainly in the recall of words when I'm trying to communicate since this is when it becomes a noticeable problem – but I suppose I may not store words to begin with. I tend to try to understanding things by visualising them because I struggle to conceptualising from a verbal description of something. An example here would be that I rarely ever read developer docs and instead just read an overview then pull the code and work out how to use it.
This holds me back significantly in my career. I find I'm extremely capable, but unable to demonstrate that capability verbally. Given that people can only base their opinions of your abilities from your ability to demonstrate them it means people often underestimate me professionally.
My dad's side of the family all struggle with this. They also find it very hard to explain things and their sentences are filled with a lot of "ums" while they're thinking about how to describe what's in their head in words.
Any advice would be amazing, especially if you've had success with this yourself. Not sure it's relevant but I am autistic. However, I suspect I have some kind of speech issue in addition to this because not all autistic people have issues speaking, and some have brilliant vocabularies.