Problem and symptoms
All of a sudden, starting January 10, 2022, the Spell Checker “WSC” dialog plugin stopped working despite the fact that previously it worked properly. As a result, you see an incessant loading spinner after clicking on the "Check Spelling" under the ABC button on the CKEditor 4 toolbar.
As it was announced more than a year ago, effective January 10, 2022, the cloud-based version of the WSC plugin for CKEditor 4 was disabled (for both free and paid users). This is an official end-of-life (EOL) date of the plugin, it is deprecated and no longer supported.
Users that added WSC plugin to the CKEditor config.js file using the extraPlugins parameter or still using CKEditor lower than 4.16.0 where this plugin was built-in by default may face an issue with the loading spinner.
To solve the issue, remove the WSC plugin from the extraPlugins parameter (if any) or disable it using the removePlugins parameter in the CKEditor config.js file:
Alternatively, instead of the WSC plugin, you can use the free version of the SCAYT plugin or commercial version of WProofreader add-on for CKEditor 4.