Context: Albeit different approaches exist for automated GUI testing of hybrid mobile applications, the practice appears to be not so commonly adopted by developers. A possible reason for such a low diffusion can be the fragility of the techniques, i.e. the frequent need for maintaining test cases when the GUI of the app is changed. Goal: In this paper, we perform an assessment of the maintenance needed by test cases for a hybrid mobile app, and the related fragility causes. Methods: We evaluated a small test suite with a Layout-based testing tool (Appium) and a Visual one (EyeAutomate) and observed the changes needed by tests during the co-evolution with the GUI of the app. Results: We found that 20% Layout-based test methods and 30% Visual test methods had to be modified at least once, and that each release induced fragilities in 3-4% of the test methods. Conclusion: Fragility of GUI tests can induce relevant maintenance efforts in test suites of large applications. Several principal causes for fragilities have been identified for the tested hybrid application, and guidelines for developers are deduced from them.