When using the A-F+- scale for any activity, when giving a student a mark through the grade book, the grade values are the opposite so giving an A grade actually gives the mark of F (screenshot 1 and 2) and giving an F grade actually gives the mark of A (screenshot 3+4). Using the override to give a different grade makes no difference. There are no additional calculations used and and the letters have their correct association marks (screenshot 6). I did notice that when viewing the grade book setup, the max grade for the letters is F where i presume is should be an A (screenshot 7). I'm not sure how to change this settings. Can any shed any light on the issue? is there a setting that can be changed or a bug with Moodle.
Yes the max grade is your problem. You can change this under the assignment settings. It is not that the gradebook is giving the opposite settings - it is that three of your activities have a max grade of 10 (which is an F) and the totals are averaging out. You cannot put in Letter Grades as the grade, you need to enter a numerical value.
Scales need to be set up from low to high, for example: F,D,C,B,A. In this example F=0 and A=4. I am guessing that you might have entered the scale as A,A-,B+,B,B-,C+,C,C-,D+,D,F. Then the A would be equal to 0 and the F would be the highest grade 10. Swap that around to: