Custom field is missing as a filter after changing the field type

After going through a modification of a text field type from 'Text' to 'String', the field is no longer available as a filter for smartlists. Don't worry, the field is not gone - it is just temporarly unavailable.

Changing the field type from one type to another is a database intensive operation and in some cases where the field values are widely populated across your database records, this can cause the filter to be unavailable until the operation is completed in full. The time it takes for the field filter to become available may vary and it can take up to ~30 hours sometimes until the field filter is available again after the type of the field has been changed.