The global bonded contact may not take care of all target areas that you expect; it only applied to initially touching faces, but for shell/shell and solid/shell the story is a bit different. Therefore, you need to apply local contact set of bounded. Two methods to find which part are not properly bonded: 1) in frequency analysis find the rigid bogy modes. 2) Perform a simple static analysis to see which component goes to space; or if you can use find unconstrained bodies (2016 and above) to find issues (wherein this is nothing but a simplified frequency analysis behind the scene to find rigid body modes). Hope it helps.
Many thanks for your assistance on this issue. All now resolved as a result of your help.