I had this happen on one of my site on godaddy after a migration with cPanel hosting. I was able to fix the issue my making them text fields and <a href="http://{{options.twitter}}" title="Twitter" target="new" class="twitter"></a>
You just need to add instruction to let user know to use only www and not http://. I have several other sites that use the URL version on my social links and I haven’t had problems with those. So I am not sure if its due to host, migration, WP version or ACF version or other issue.
Advanced Custom Fields PRO Version 5.4.4
Timber Version 1.1.5
