The error message, "An existing File Geodatabase item was found with the same title, <file_geodatabse_name>, Please choose a unique title and try again." is returned when exporting a hosted feature layer with a similar name to another exported file geodatabase from a different hosted feature layer.
Edit the file geodatabase name to resolve the error when exporting.
Export the hosted feature layer with a shorter name first. For example, if the names are 'sample_name_layer' and 'sample_name_layer_second,' export the 'sample_name_layer' hosted feature layer first.