History New Value [sys_history_line.new_value] truncated to 40 characters and so does not Sys Audits New value [sys_audit.newvalue]. This prevents features like SLA History Walker from supporting GlideList field type as GlideList is a comma separated list of sys_id values. each sys_id is 32 chars long, so if more than one value is stored in a GlideList History New Value [sys_history_line.new_value] stores on valid sys_id, followed by one corrupted sys_id and no other values for the remaining records.

SLA Repair and SLA Timeline are both affected by this platform defect on GlideList.

1. In any form add more than one value to a list field, e.g. on incident form add two people to watch list field.
2. Compare History New Value [sys_history_line.new_value] to Sys Audits New value [sys_audit.newvalue]
Expected: History New Value [sys_history_line.new_value] to be identical to Sys Audits New value [sys_audit.newvalue]
Actual: History New Value [sys_history_line.new_value] is truncated to 40 chars

1. Change the dictionary on History New Value [sys_history_line.new_value] from 40 chars to 4000 chars. Do the same for History New Value [sys_history_line.old_value]
2. Go to: Table Rotations. Select sys_history_line. Click UI Action: Synchronize Shards.

If the issue you are trying to resolve relates to SLA Repair and was caused by use of a platform GlideList field that was truncated then after completing the first two steps:

3. Run the following command in scripts - background on any record that has a task_sla with a broken SLA timeline. This rebuilds the history set and history lines for that incident.
new GlideHistorySet("incident", "<incident.sys_id>").refresh();
4. On the broken task_sla run UI Action: Repair.