Filter Restrictions for Text Area (Long) Fields in Salesforce

Filters applied to standard Text Area (Long) fields only permit the first 1,000 characters to be searched.
Filters applied to custom Text Area (Long) fields only permit the first 255 characters to be searched.
If the filtered value does not appear within the character limits identified above, the filter returns false and no matching records are returned. This can cause confusion when filtering on long text fields where the relevant value appears after the character limit.
Recommended approach: If you need to filter on content that appears beyond these character limits, consider using a different field type (such as Text or a Formula field that extracts the relevant portion).