I'm still having this issue and I've upgraded to 4.7.2. I've searched everywhere and can't find a cause. I'm not getting any error the activities just don't show in the list.
I upgraded to 4.7 without any issues. The Activity dashlet doesn't show any activities nor do activities show under the contact tab. I did a search a found there was some error causing this and it was marked as fixed. It was related to running php 5.3 but I'm running php 5.5.29 on civihosting.
What's causing this?
https://forum.civicrm.org/index.php?topic=36800.0
I do not get a datatables error. I get no error at all. If you look at the screen grab, notice it says, Showing 1 to 11 of 11 entries but no activities are showing. 
Also see the screen grab for the Activities tab in the Contact. 
