Issue
When openning the Workflow designer, all the actions are missing from the left side panel.
Resolution
1- Remove your user permission on the site level then remove it from site collection level.
2- Re-add your user back to the site collection and site level.
3- Under Site Settings page, under Nintex Workflow, click Allowed workflow designers and make sure your account is listed as an allowed designer.4- Check in Central Administration -> Nintex Workflow Management -> Manage Allowed Actions.
Additional Information
This happens sometimes after the user hasn't been accessing the site for a long time and user permissions has been changed.