Not sure if this is considered rude or not

[Unitedstatesofwhatever1]

Sometimes if I misunderstand something my partner says or mishear, he will scrunch his face up at me or frown and say 'What's going on right now?"
In a 'is something wrong with your brain?" Sort of way.
It's hard to explain but I just find it a bit sneery and patronising.
Sometimes people don't explain things well or loudly enough. You ask them to repeat or clarify and they say, "Sorry I said/meant X."
That seems to be how a normal converse would go.
It's almost now like I am afraid to not understand something and it is making me think something is wrong with me .
There are many people he would never dream of doing that with, though.

That's your answer then - he doesn't do this to other people, he's trying to make you feel stupid.

He's also had some work issues recently and when I've tried to be positive and supportive sometimes he's a bit short with me and says 'yeah! Ok! Don't want to talk about it '

Then was talking about it to his family for an hour yesterday.
His Mum gave him a piece of advice which was the exact same advice I'd given him, he got defensive when I asked if he would follow it.

This does sound patronising. We all mis-hear or misunderstand things sometimes! Try saying "no need to be rude" when he says it.

Beyond rude. Does he even like you?!!

He does seem to realise it but keeps doing it. I will just have to keep being firm

He sounds insecure and patronising.

Or is it putting with his choice of words "I think I've misunderstood something because I haven't got the point you're making"

It’s hard to say. But it’s upsetting you and he continues to do it. So it doesn’t really matter wether we think it’s rude or not.

My partner will often ask where I am. Usually, that’s because if I mishear or don’t understand what he is saying, my brain is completely focussed on something else. But I have adhd and still grieving the death of my mum. While ‘where are you’ could be interpreted rudely, I know dp means it kindly and offering an opportunity for me to talk to him. Rather than berating me for not listening.

If I found it uncomfortable and he kept doing it and I told him so, it would be rude.

He is a little insecure about his speech I think, sometimes he'll make large pauses before finishing sentences, but I'd never mock that or anything, he can't help it.

It's almost now like I am afraid to not understand something and it is making me think something is wrong with me

Do not internalize his shitty behaviour as something being wrong with you. That is how you end up staying in an abusive relationship, always trying to second guess what is going to cause a reaction and hiding your true self to try and avoid being negatively judged.

In a good relationship, the conversation would be exactly as you describe above and say “That seems to be how a normal converse would go.”

This behaviour will just get worse and worse. Stand firm with him, put him back in his place or move on! It's not the way to speak to someone you love.