MR changes became more

in Gitlab

1. Created a new branch called ‘xxx’ from prod.
2. Coding in the ‘XXX’（2 changes）
3. Created a new branch called ‘merge_XXX_dev’ from dev.
4. Pull from ‘XXX’ to ‘merge_XXX_dev’ and commit the changes（2 changes）
5. Created a MR (‘merge_XXX_dev’ to ‘dev’) and ask other team to admit it (2 changes)
6. 2 Days later when my MR turns there were 194 changes in my MR(during the 2 Days other team’s changes appeared too)

I want to know the reason and how to avoid it again.

can anyone help? thanks!!