I am getting "The theme used in the app is newer version". From what I read from Geonet forum, the only solution is to wait for newer version of web appbuilder. I do know a way to work around it but I am just curious to know when will the newer web appbuilder will be released.
Typically the developer edition is released 4-6 weeks after the online version. The Portal version is after that.
With the UC right around the corner, sometimes timing changes some as they try to push versions (i.e. AGOL and 10.5.1) out before the UC so people can start playing with it before they go.