Additional processes could also include:
- case assignment
- lead assignment
- case escalation
- approval process
This help article here explains when the 2 dates are different:
LastModifiedDate is the date and time when a record was last modified by a user, and SystemModstamp is the date and time when a record was last modified by a user or by an automated process (such as a trigger).
As a result, LastModifiedDate and SystemModstamp will differ when
automated processes update the records, which will happen in the
a) The archive date is extended to greater than 365 days.
b) An existing picklist value is updated.
c) A contact's e-mail address is flagged as per the Email Bounce
d) The LastActivityDate field is modified
Additional comparison with performance tips can be found here:
What is the difference between LastModifiedDate and SystemModStamp?
Let’s recap what LastModifiedDate and SystemModStamp dates are. They
are both system fields that store date and time values for each
LastModifiedDate is automatically updated whenever a user creates or
updates the record. LastModifiedDate can be updated to any back-dated
value if your business requires preserving original timestamps when
migrating data into Salesforce.
SystemModStamp is strictly read-only. Not only is it updated when a
user updates the record, but also when automated system processes
(such as triggers and workflows actions) update the record. Because of
this behavior, it creates a difference in stored value where
‘LastModifiedDate <= SystemModStamp’ but never ‘LastModifiedDate >