Hi folks,
We just fixed a critical issue!
There was a bug in the REST API - Head Tags plugin that was causing some REST API calls to respond with unexpected 301 redirections. Also, those redirections were failing because the Access-Control-Allow-Origin header was not present and were making browsers to show a CORS error in the dev tools.
It was reported here some days ago but it took us some time to realize that the problem was in the plugin.
Remember that if you are using the REST API - Head Tags plugin, you should update it to the last version (using the update button in the WordPress admin panel or downloading it from here).
Feel free to ask if you need some help or have any questions. 