This was NOT acf related. Really sorry for this, it was either an update of WPML or when we added Danish and German languages that caused the problem. It converted all permalinks from for example: Allmänt -> allmaent. Before it was Allmänt -> allmant.
We solved it by:
a. Defining: ‘menu_slug’
b. Adding a filter that solved the permalinks problem
If anyone need the solution, please contact me.
Thank you for the quick help ACF and sorry again!
Marking this as solved.
