No wp-admin, wp-config, or .htaccess folder/file

I had this happen once, and the solution was actually quite odd. This may or may not help. After going through all of what I thought was obvious, it ended up being a plugin conflict with a slider revolution add-on. I racked my brain for a couple of hours, then started deactivating plugins on a whim. Something with the media I had uploaded caused the issue, but I can’t put my finger on it to this day. I’m aware this is an extremely unconventional answer to the question you are asking.

Ever since that crazy night, I always start deactivating plugins to determine if there may be a coding conflict.

Hope this helps.