3 of us here so far have encountered this annoying little bug (I assume) since updating to the latest R20 version.
Sometimes the object manager column slides left so only the last few tags are visible and not the objects themselves. (see below). We can eventually click on the divider to slide things back, but its always hit or miss and takes a minute or 2 to fix. Sometimes restarting cinema fixes it. (re loading the user setup doesnt)
Not sure what triggers it.