If you opened Studio One prior to having your VocaLign plug-in activated in your iLok License Manager, it is possible that VocaLign has become blocklisted. Here are steps to resolve the issue.
1. Open the iLok License Manager which is downloaded from iLok.com and verify that you have your license activated for VocaLign. If you do not see the license and you purchased it from PreSonus, please submit a support ticket from your account.
2. Open Studio One and go into View>Plug-in Manager.
3. Once in the Plug-in Manager, remove VocaLign from the blocklist or clear the blocklist entirely.
4. Re-start Studio One and test for the issue once more. If the issue persists, please go back into View>Plug-in Manager and choose the option to remove plug-in settings. Re-start Studio One and you should be all set.
Here is a link to the Synchro Arts download page.
Here is a link to Synchro Arts' article on this exact issue.