On the Activities page, the dates you see at WBS level are aggregated from the activities belonging to that WBS node.
On the EPS page the dates you see are those which were stored the last time the project was summarized.
The start date visible at the project or WBS level is the earliest early start date for all activities in the project or WBS. The finish date visible at the project or WBS level is the latest early finish date for all activities in the project or WBS.
The planned dates at the project or WBS level are the earliest planned start and latest planned finish respectively for all activities in the project or WBS.