In MDL-39990, Fred noted:

"On 2.6 and master, the recent activity block does not display the updates in the pages themselves, even for a user that has access to those pages. 2.4 and 2.5 do."

Marina analysed:
"1. this is a regression from: https://github.com/moodle/moodle/commit/6d3d9bd927d5386b1dc4fbbcb7db5559efa7a5cd , this commit does not make any sense and should be reverted - wiki_subwikis.userid is not an author of the change and is null unless this is an individual wiki."