I would carefully review the method and especially the GC configuration (Gas type settings). Method resolution can be triggered when the GC has had a gas type change in the configuration, column dimensions or gas type to the column has changed. In some cases a hardware problem where the instrument no longer has a function that it used to control such as make up gas etc. With your description it appears to have been at least two changes. Please let us know what you find out. Once resolved , the method will need to be saved to stop the method resolution process from happening.