This error is caused by having numeric type columns in your Posgres table which did not have the precision or scale specified. Dremio 4.1.x will now simply truncate the values in this column to the smallest scale it encounters instead of throwing the error.
You can also fix this by altering the Postgres table to specify the precision and scale for the numeric columns where they are unspecified (e.g. column_a decimal --> column_a decimal(38,16))