After updating the Entity Framework model, all mapping data is deleted

Question

I reopened an old project that uses entity structure and model generation, but when I update the model, all mappings are deleted.

I need to add a new model to the model, but I can not do anything with this problem. After adding the table, I have an error regarding the missing mapping:

"Error 113 Error 3027: No mapping was defined for the following EntitySet / AssociationSet - Table 1, Table2 [...]"

Has anyone had this problem?

For information, I use .NET 4.0, EF 6.1.3, Mysql connector 6.9.7.