Validation schemas used are from the schemas project, so if the schema name is correct, please file bugs directly there.
Schema type assignation is done purely on the filepath, without looking at file content. This means that playbooks are identified only when they are inside a folder named playbooks. The same applies to vars and tasks. If you do not follow the official Ansible code layout guidelines you will not be able to benefit from all of the features. In some cases, unfortunate file or directory naming could confuse the tool to make it attempt to use a different schema. You can override the default file patterns used to determine which schema is used in your vscode settings.json.
Please check changelog page for details regarding each new version.