1. Try recompiling the code to ensure all necessary classes and interfaces are generated correctly.
2. Review any custom or third-party modules that may be interacting with the VariableResolverInterface. Check for any missing dependencies or conflicts that could be causing the issue. Disable or remove any recently added modules or extensions and see if the error persists
3. If you have made any customizations or overrides related to the VariableResolverInterface or its implementing classes, double-check those changes to ensure they are correct and do not introduce any errors