I have trouble putting my thoughts into words sometimes. It happens even when I'm completely calm and alone, and I haven't noticed it being any worse in company, in fact it's probably better with individuals I feel good about, maybe worse in groups that habitually talk quickly and / or competitively, though I avoid those fairly well and when I can't, I'm usually resigned to staying pretty quiet.
So in me it feels like an annoying technical hassle, as if the mentalese to English translator in my brain has balked at a job. If I remember, I try to give it another go later, and there's not much that doesn't eventually unscramble into words. I often find that what felt like a small mentalese thought can take a lot of English to express it. But I also have trouble describing some visual (3-dimensional?) problems I'm solving, such as how to make a warped cupboard door close straight. I guess that's normal though, pictures being worth a thousand words - if I keep writing it down and editing, I get there. So I think the cause of the difficulty might be just that there's a lot to process. I've also noticed that it can take a long time to make sense of old written notes about some tasks, notably special interests when they get technical, even though I was doing my best to write it clearly, but short of time.
Thoughts about emotional and interpersonal matters can take a long time to express in words. I remember trying to express my thinking about a couple of incidents I'd been through that were similar in character, and had both led me to feel uncomfortably resentful. Something hit me that took a few days before I could express it. The resentment had been long gone and I didn't feel uncomfortable exploring it, it was just annoyingly difficult to put it into words, but I got there, and I felt it was a bit of a step forward, I learned something about myself that I hope will be useful for making those negative feelings less likely.
I think a lot about things I can't yet understand, and if I can't understand a thing, I can't put it into words. Writing it helps me to shape it into something coherent and intelligible. I should use drawings more.
I think I've just got a slow thinking style sometimes, which is incompatible with being rushed, other times it's fairly quick.