New Target Standard users cannot see activities, incorrect access rights

We have invited 15 global users to the Marketing Cloud and provisioned them with access to Adobe Target Standard. Several have accepted the invitation, created a login, and successfully logged in to Target Standard. Once they successfully logged in, we upgraded their access rights in Standard (under Setup / Users) from Observer (the default) to Approver. Unfortunately, none of these users (who are located in Korea and Singapore) can see any activities listed under Activities when they log into Target Standard. Also, the Create Activity button is grayed out even though they have Approver rights. Any assistance re: what may be causing this issue would be greatly appreciated!