Weird. Mine show up fine still. Make sure your browser is at 100% zoom, try refreshing, as a last resort clear your cookies. If it still persists, report the bug to bubble.
I got the same issue few weeks ago and did everything mentioned by @J805 with no success. Well, I kept calm and things magically worked again, but there really is this bug.
@Newed Mind miraculously reappeared as well. Not going to mark this as solved because as you say, there is definitely a bug here.
For any that come upon this note - you should also know that I tried several different Browsers to make sure that this was not a environment problem (e.g. a problem with me having rubbish in my cache). The issue cut across three different browsers.
Editor bugs like this happen around time Bubble pushes an editor update. Takes a while sometimes but it usually corrects itself. File a bug report if it lasts a long time.