Good day. I am experiencing an incorrect grading on the multiple choice test questions.

If, for example, the question has seven (7) answers of which four (4) are correct and only some of the four correct answers are selected the score calculates correctly - eg 3 / 4 or 4 / 4 etc

If however any one of the incorrect answers are selected the score defaults back to 0. It does not matter if the student selected 3 correct answers, he still receives a grading of 0.

I have checked the scores linked to the answers and we are not implementing negative marking. The incorrect answers have a score of 0 and the correct answers a score of 1.

What could the problem be?

Below is a gift export of a simple multiple choice test with this exact behavior:
// question: 39860
::::[choice_multiple]Select 1, 3, 5, and 7{
=1
~2
=3
~4
=5
~6
=7
}

Forma version?

I believe this bug existed in one of the previous versions. It has been fixed long ago. If you upgrade your LMS to the latest release the MC question will be working as expected. If you browse into the changelog of the different versions you should probably find the reference.

Is such a gift file generate a choice multiple question or a single choice question?

It seems your file is not respecting gift standards.
Check https://docs.moodle.org/402/en/GIFT_for ... ht_answers