For everyone having a problem with upgrading to RC2, do what I did and maybe it'll work for you. Yes modules disappear which is why you have to refresh but don't install them all at once.

1. Install language modules FIRST.

2. Upgrade to RC2.

3. Install the rest of the modules.

NB: For some reason the only module I cannot upgrade is the Playr module. I hope it'll be downloadable on the final release of 11.