Just now I reseted the permalinks to show only post name, it was previously set to Month + post name.
I deleted that blog folder again, so at the moment, my blog page is showing. But I bet that folder will create itself again within a few hours.
Oh portfolio didn’t show anything because I have Jetpack’s Portfolio enabled, but didn’t create any projects. I created a sample project and now that page is showing. Hmmm, if Jetpack’s Project page is overriding my portfolio page, then maybe Jetpack is doing the same thing with my blog page.