This issue has been resolved and reassignment functionality is back up.

We are currently investigating an issue where the reassignment functionality is not working correctly for both Google and Microsoft customers. This issue happens from both reassigning from Google/MS outlook and a Salesforce button.

If you need an immediate solution for this, the workaround so that you are not blocked is to create a net new meeting and cancel the original event. We will provide updates as soon as possible as we work to get this resolved.