Have you been editing any YAML files associated with that job or on the host of the Jenkins? This error occurs only if a YAML config file is configured improperly.
"This YAML error is typically caused by incorrect indentation or nesting of data structures. YAML relies on indentation to denote structure and relationships."

https://www.geeksforgeeks.org/how-do-i-resolve-a-mapping-values-are-not-allowed-here-error-in-yaml/