"unable to proceed because of an error from the data source" when I use a created calculated field.

I have created a data source from a PostgreSQL in tableau server as

under Explore/Default->new-> workbook

Connectors->credentials->PostgreSQL->credential -- this list all the table in the database.

drop a table from list of tables to the mid panel.

Connection works here, and on update I see the content of table.

I switch to Sheet1, I see all the columns names

If I drop the content on the Rows and Column space, i see the chart.

I create a new calculated field

ex.parameter name: calc with value [col1]*100

if I go back to Data Source page, I see the columns 'calc', and updating shows the value of the new column,

However if I refresh the table by clicking on refresh button I get this error.

Unexpected Server Error
TableauException: An error occurred while communicating with the data source
2021-09-08 17:40:46.808
(YTj1mSE4eJx3BMQEnxEXEgAAAJc,1:1)

After this update on table does not work. the table can only be updated or refreshed if the calculated field is deleted.

Observation 2.

If I try to use the calculated filed in the work sheet, I get error

unable to proceed because of an error from the data source
try connecting again. If the problem persists, disconnect from data source and conact the data source owner.
 
An error occured while communicating with the data source.

Observation 3. If the calculated filed contain the actual column name without any manipulation. all works just fine. But editing and changing the same filed brings back the issue.

Note: I have other data source in the same Explor/default, they are using the same database, with the same authentication. They are working fine.

I tried to create the new data source using tables, that are already in use by other data source, but I faced the same problem. So I don't think there is any problem with table or database connection/authentication.

Is there any restriction on how many data source we can in tableau server? At present I have 4 data sources, which are working fine.

Has anyone seen this issue? Please help in fixing this issue, it is blocking me in my work.