With 20.3.1 & 20.3.2 the option to create historical reports and the SLA History section is missing from SLA reports.
Release : 20.3
Component : 99991231 UIM OPERATOR CONSOLE - SLM/SLA
This will be resolved in an update coming after 20.3.3.
Here is a screenshot from the SLA that does not show any option to see the Historical data:
This image shows the section now missing from the SLA report PDF.