This exact same issue is happening for me as well while using a container and setting it to full width as well.
I ended up just going back to the Hello Theme menu instead which is above.
My whole WordPress environment is up to date including core and all plugins.
I noticed in previous replies to this issue months back that because Flexbox was still in Beta, that the advice was to use sections instead but Flexbox has been stable for a while now so do you think this will be resolved?
