SOLUTION : Again I got this error, even when trying with the Sitecore instance CD URL now.
Correcting the Server Name in the following tables of the Shard Databases for my Sitecore instance fixed the issue
DATABASE NAME > TABLE NAME > COLUMN NAME
sc92_Xdb.Collection.Shard0 > _shardManagement.ShardsLocal > ServerName
sc92_Xdb.Collection.Shard1 > _shardManagement.ShardsLocal > ServerName
sc92_Xdb.Collection.ShardMapManager > _shardManagement.ShardsGlobal > ServerName
The error details (An item with the same key…) were not enough to resolve the error, because there were no two fields with the same field name in the Forms item. When I checked the XConnect logs, we found that there was a problem in the xDB connection as below:
network-related or instance-specific error occurred while establishing
a connection to SQL Server. The server was not found or was not
accessible. Verify that the instance name is correct and that SQL
Server is configured to allow remote connections. (provider: Named
Pipes Provider, error: 40 - Could not open a connection to SQL Server)
That was why adding a contact to xDB (form’s custom submit action code does that) or listing the contacts in the Experience Profile was throwiing the above errors.
After correcting the server name in the above three tables, the Experience Profile error was resolved and the form submitted without any error in the browser console.
Special Thanks to : http://sitecoreworld.blogspot.com/2018/11/error-xdbcontextloggingplugin.html