Unreal allowing editing of files that are not checked out.

While I’ve been working on this project for months and using Perforce without trouble, lately I’ve been sometimes receiving the following warning when saving some assets. Other times I can save those same assets without issue.

I’ve tried setting my /Content folder to read-only as some advice suggests, but to no avail. I’m left just manually checking out those items through the right-click menu.

Does anyone have a remedy?