I just got our last user onto LEX, and he needed help locating where past emails show that sales reps sent. I showed him past activities on the contact and account level, to my dismay, his view of past activities was empty. This is in reference to at least one particular contact/account btw. I'm able to see the two emails sent/logged from about two weeks ago, they were sent by a completely different user, so not this new LEX user or myself. The user having issues has view/modify all data, as well view/modify all data for all objects as well. I've checked the organization-wide sharing settings, account : public read/write, and activity : controlled by parent. I'm at a loss, all settings point to this user being able to see/modify any data they want.