WordPress 5.5 update triggers PHP notices in Toolset Blocks

Symptoms

The update to WordPress 5.5 triggers the following PHP notice in the error logs:


PHP Notice: register_rest_route was called incorrectly. The REST API route definition for toolset-dynamic-sources/v1/dynamic-sources is missing the required permission_callback argument. For REST API routes that are intended to be public, use __return_true as the permission callback. Please see Debugging in WordPress for more information. (This message was added in version 5.5.0.) in \wp-includes\functions.php on line 5225


Workaround

The latest hotfixes resolve this notice which appeared with WP 5.5