Seen this a couple of times now.
Just know that something DO use credentials, so following this guide COULD remove access to those things.
This is just one solution that I’ve seen for it, and if that doesn’t work: factory reset is a must.
Under Settings > Security, you should have Clear credentials enabled. I haven’t experienced this myself on a m7 so I can sadly not show a screenshot on that too.
Simply tap Clear credentials, it will ask you if you want to remove all contents. Tap OK. It should now be ok, with Lock screen enabled. You might have to restart your phone, but this should work. If not? Factory reset.