We have deactivated some of the wsp from our office 365 sites and in one of wsp code, feature deactivation logic maps system master page to v4.master. This has an impact on OOB pagelayouts (pagenotfound.aspx,articleleft.aspx and others)
I tried to map system master from site settings --> Master Page --> Applied seattle.master to system master page section. But no luck, it is still pointing to v4.master.
Need some help or pointers to map the seattle.master to OOB pagelayouts.