I manage a couple Concrete sites (on two different servers, hosts, etc.) and I have updated both to 5.4.2.1 last night with no issues.. See an interesting thing on one of the servers: In Dashboard, I see "Theme Options" and in there I see an option for "Social Networks" and "Mobile Themes." I don't see this as an option on the other server - am I missing something? Is this because I enabled composer beta on that site?

Thanks,

Kent