Map bubble colours and size

Hello

I've created a map plotting values by longitude and latitude. I've varied the bubble size according to the the size of the value and I also want to change the colour, blue for low, red for high. However, although some variables show the large bubble size as red and the small ones as blue (which is what I want), some variables are showing the colours the other way round: red for small, blue for large. I can't seem to change this to make it consistent.

Has any one else had the same problem and is there a fix?

Version: 2.123.742.0 64-bit (November 2023)

Thanks.