dbt snapshot is trying to add column that already exists in table

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I firstly created the table using a model for past data and then when I tested snapshot it gave me this error.

Field fieldname already exists in schema

When I look at the logs I saw this:

Adding columns ([<BigQueryColumn fieldname (STRING, NULLABLE)>]) to table `projectname`.`dataset`.`tablename`".

Why it tries to add column that already exist? Is there anything to avoid it?