The timeline shows all your activities with a date next to it. This is perfect, but this actually is the date the record was modified. So after re-assigning an account, all records are also transferred to the new owner (which is what you should want), but afterwards the timeline shows on all activities the date that the record was re-assigned.

This is very confusing, because when another sales person is going to look at this account, he or she only sees 1 date next to all activities and has to specifically open the record to see when it was actually created. (which most of the time is the most relevant date). And actually, email records don't even show the 'created on date', so after re-assigning, nobody knows when the email was sent.

This is a very bad design. The solution provided by Microsoft is to alter the relationship so that activities are not reassigned, but this is a terrible solution. (Re-assigning records like leads is very often part of the lead management process and when a sales person is off-boarded and records are re-assigned, you want the new owner to be responsible for this data. It also collides with security settings, because users might not be able to see records from deactivated users.)

Solution: For once, make the timeline actually chronological, by showing the created on date instead of the modified on date. Or perhaps show both, but not only the modified on date.

This issue has persisted since 2013!, I don't know of any other CRM system that handles it this way and it takes away all the insights from the timeline. So in my opinion this is something that needs to be fixed ASAP.

Other topics/users referencing the same issue and lacking support:
https://social.microsoft.com/Forums/en-US/a5d124c3-1837-4c60-a6dd-946d27783602/ms-crm-2013-social-pane-phone-call-issue?forum=crmdevelopment#e41c7a46-5c61-439d-bc3e-92eb690f8714

https://community.dynamics.com/crm/f/microsoft-dynamics-crm-forum/137978/all-activities-wil-be-set-to-date

https://community.dynamics.com/crm/f/microsoft-dynamics-crm-forum/291708/activity-dates-changing-when-owner-is-update/837248

the last two topics contain helpful screenshots of the old interface. Below are 2 screenshots from the unified inteface, where the same thing happens:
Before:
https://imgshare.io/image/N8RCYP
After:
https://imgshare.io/image/N8R5MQ

notice that the appointment stays the same, because this is the 'due date', but it is still moved to the bottom while it was previously on top. This also makes very little sense from the user experience point of view.