CoreMedia Multi-Site is designed to allow concurrent editing, while localization workflows are in progress. Having this, it especially allows editing master as well as derived contents, while an external translation agency takes care of translating them.

Nevertheless, concurrent editing may conflict with your recent changes. Because of this, CoreMedia Studio will show a hint in a nagbar, if your changes may collide with translation results. The nagbar will be shown for both roles of a content within a translation workflow: as master or derived. The relevance for the nagbar is different according to the roles, though:

As editor of a master content item, you should not start a new localization workflow, if another workflow for this master and the same target locale is already running. While sometimes intended, it may result in unexpected translation results since, for example, the workflows may not be handled in the expected order.

As editor of a derived content, you may expect translatable properties to be overwritten soon, when the localization workflow, for example, uploads the translation results. Depending on the robustness of the localization workflow, it may also fail (in other words: escalate), when you have checked out the content while the workflow tries to apply the localization results.

Long story short: If the nagbar appears for a given content, ensure you are aware of your editorial processes and take actions to the content with care.