I am experiencing the same thing on Android. I cannot complete the color challenge at all. The four bot battles are laggy and extremely buggy (abilities that should trigger in the red deck do not work correctly at times mostly) but I can at least complete them. Cannot complete the last battle for any of the colors that is supposedly against a real player though. It read the error unable to join event message again and again. I uninstalled and reinstalled the game, have opened and closed it multiple times and given it days to be patched to no avail.
I am experiencing the same thing on Android. I cannot complete the color challenge at all. The four bot battles are laggy and extremely buggy (abilities that should trigger in the red deck do not work correctly at times mostly) but I can at least complete them. Cannot complete the last battle for any of the colors that is supposedly against a real player though. It read the error unable to join event message again and again. I uninstalled and reinstalled the game, have opened and closed it multiple times and given it days to be patched to no avail.