And I finally figured out why. I think some of these custom ROMs have built-in adblockers. Medscape won't install and work properly when these adblockers are active. It says something about internet connectivity issue. Anyway it took me awhile to figure out why Medscape wasn't working, so if anyone else was wondering why, I thought I'd share the info. The same problem arises when I install adblocking apps on stock EE4 too.