Thanks for writing in.
I believe that there are 2 reason why this is happening. Your X or Pro is not updated while your cornerstone is the latest version and plugin conflict because mobile button is run by script.
Check the latest version:
Plugin conflict test:
You can do this by deactivating all third party plugins, and seeing if the problem remains. If it's fixed, you'll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
Let us know how it goes!