The cross-version compatibility checking mechanism is triggered when a project with new feature usages is loaded with an older version of the modeling tool. The mechanism tracks feature usages of the 2021x R1 version, which results in the appearance of a Missing features detected notification in earlier modeling tool versions. The following table shows tracked features, the version they appear in, and whether the project can be committed/saved without any consequences. 

If you are working with features that can cause inconsistencies after save/commit (see the table above), the following warning message indicating possible consequences if you proceed will be shown.