Yes, processing can still be an issue even though they excel at school! DD2 got all As and A*s in her GCSEs; but she does not understand conversations, books or films! She worked three times harder than her school friends, and she is very bright! However, the effort by A level was exhausting for her and she lived on filter coffee to stay awake to achieve it.
The problems get more apparent, the higher they go up through school. Primary is not too much of a problem for a bright child; secondary demands more by way of complex language, planning, remembering where to go and what to do and with what equipment....
DD told me she never had any idea what to do in science experiments. She switches off in conversations, with anything more than short answers to her questions. She switched off as the teacher told them what to do. She then asked her classmates what to do. They explained, but she switched off again. She asked her classmates what to do again - they got annoyed with her and refused to explain again! She was left with no clue what to do!
There is no point getting annoyed with them for not following instructions - it could be poor attention and/or poor processing and/or poor working memory.
Is there a subject that bored you rigid at school? For me, it was physics. I could barely force myself to get through GCSE. If I had to sit through degree level physics lectures, I would be so bored with it, way over my head and beyond my ability to be interested, I would switch off! That's how conversations or books or films are for them, and getting cross with them, does nothing to solve the problems they have! I just never did physics at university, because adults get to choose to avoid things, they are useless at. Children don't have that choice - with SEN children, we need to enter their world and imagine what it's like for them.