Hmm ok… taken a look and nothing obvious pops out except that there are a few errors in the console coming from your layer slider. I’m wondering if there is a conflict there? Could you please try deactivating that plugin and see if the sticky side buttons show?
Failing that, you may need to do a full isolation test. ie Deactivate all other plugins and switch to the default theme for testing. Do the buttons show? If yes, then reactivate things one by one, testing in between, to determine the culprit, then reply here.
Thanks,
Maeve