Not a bug
Sometimes you can find yourself taking over a project using WPML which has not received any maintenance for years. Of course, you will want to update the WPML plugin in the safest way possible.
If you are not able to upgrade WPML plugins directly from the current version to the latest one available, you should probably do it step-by-step.
In this case, we recommend the following steps:
0. Backup your website and database.
1. Deactivate and delete the “installer” plugin (if you have it).
2. Deactivate all WPML plugins.
3. Remove all your WPML plugins.
4. Open a support ticket requesting access to the following folder.
5. Download and install the closest major version to yours. For example, if you have WPML version 3.9, update it to 4.0.8.
6. Activate your WPML plugin from the Plugins page in the WordPress admin.
7. Complete the setup, if needed.
Repeat this procedure and update WPML one major version at a time.
Once you have the latest version of WPML, install the latest versions of the rest of WPML add-ons.