I added a data filter to my custom dashboard in Explore. When I attempt to apply a filter value while editing the dashboard, I see the error Network error.
The error Network error is displayed when the dataset or report associated with the filter has been removed.
To resolve the error, remove the current filter and add a new filter. This will ensure the new filter is linked to a dataset for the current report on the dashboard.
For more details, see the article: Best practices for using dashboard filters.