I have been watching this thread in detail, as like the OP, my dd is too very changeable with her maths and like OP, I too have been doing work at home on this to help.
One day she seems to work fine and has no problems, next day, it all seems to go out the window - yes I got extremely cross last week (I posted about it), which wasn't my most proudest moment, I have to admit.
I am not a teaching professional, just a Mum doing her best and worrying that my dd is struggling and want to help. So I want to let the OP know you are not alone!
I too have asked my dd's teacher if there may be other issues, but like CarrieMoonBeam says, I have been told there are no other indicators at present to suggest anything and they would not be worrying about this until Year 3.
I was also told that it is perfectly normal for children in Year 2 to start to show fluctuations in their learning, as they find the work more challenging. My dd's teacher said that some children just need that little bit more time to mature than others when it comes to learning and concentrating, but in her experience a little extra support gives them the confidence that they need and then they are usually fine, I know dd is getting some extra individual help with maths at school.
Obviously, you may know of other issues with your child and to be honest, I wouldn't be surprised if my dd had dyscalcula or something, but I think it is being faced with 'sums' that makes my dd panic, could this be the same for yours?
Yesterday we were chatting about making money and she told Daddy she would sell him her bag of toffees for £10, I said but you only bought them for £2, so that was a big profit and she replied quick as a flash without even thinking, 'yes £8!' If I had put that sum written 10 - 8 = to my dd yesterday (bad day), she would have had to think about it and maybe count back, even though she knows her number bonds.
I am now trying to do more practical things than sums, just to boost her confidence, although have subscribed to Mathsfactor, which has placed her at subtracting 1 and 2 to start with (I thought this too basic but is great for her confidence) - she loves it, but that is another thread!!
I am in the 'don't worry just yet' camp, but keep talking to the teacher, so they know you are receptive to any extra help and supportive at home.