I think so too, it must be a bug in Enfold 4.5.4 – Everything worked fine in 4.5.3 and I didn’t add or updated any plugins or other code, only Enfold.
I have the same problem: can’t switch to the normal front-end to see my changings and only see the maintenance page – even with the preview function. Using Enfold 4.5.4 / WP 5.0.3., classic editor enabled. Maintenance Mode enabled.