It appears that, following the last upgrade, items which previously showed on an individuals activity log now don't show up. A colleague sent out an email which was assigned to a case. The email shows on the case but not in the colleagues activity list. This list is used as a record that we can refer to as a quick check if something has been misassigned or that we did remember to do something. What was the reason for this being changed and is it something we can choose to bring back?
Yes this was changed recently. I preferred it the old way too, but there was a feeling that it was duplication. See https://github.com/civicrm/civicrm-core/pull/12620