Overview:
Long Text Area field cannot be displayed completely in Salesforce report. The report shows only a limited number of characters of the Long Text Area field.
Root Cause:
There is a limitation for the Long Text Area field that the user will be able to see only 255 characters on the report.
Solution:
If the user exports the report, it will provide the complete data of the Long Text Area field.
Please refer the Idea link that will provide more information on the same issue:
More than 255 characters in a Long Text Area Custom Field is not visible
Related Documentation:
CRM Help Documentation: N/A