Currently if you try to enter a value longer than 255 characters in a parameter field in a policy's script payload, the JSS will automatically cut off everything beyond the 255th character. This used to be a limitation of MySQL prior to version 5.0.3, but it no longer is. You can store up to 65535 characters in a Text data type field as described in the MySQL 5.5 Storage Requirements document: https://dev.mysql.com/doc/refman/5.5/en/storage-requirements.html
I referenced MySQL v5.5. Because at the current time that's the minimum version the JSS 9.97 requires, although it recommends v5.6. http://docs.Jamf.com/9.97/casper-suite/administrator-guide/Requirements.html
Can you please increase character limit for parameters to 65535?