Hi Nathalie,
Thanks for writing in! First of all, please make sure to clear all caches and test your issue again (https://www.wpbeginner.com/beginners-guide/how-to-clear-your-cache-in-wordpress/).
If the issue persist, then you need to disable your 3rd party plugins except Cornerstone, Slider Revolution to see if you’re experiencing any plugin conflict. If the issue resolved, then you can activate your plugins one by one to see which plugin causing the issue.
Also you can check the following thread and see if you’re having a similar issue (https://theme.co/apex/forum/t/anchor-links-dont-work-in-mobile/53899/3).
If you’re still having issues, please provide us with your WordPress login credentials in a secure note to check your issue further.
Thanks!