Had the same problem today. Could not summon b2 or brute. Healing worked.
Imagine being a small guild doing that mission on the last phase because you have not enough power for all the phases. Some players have left for the big guilds and new recruitments are unsuccessful because of your GP. Then you do at least that mission to get the Shards and guild token 2 to stay a bit competitive and lucrative. Then you can't summon one important character in the fight, lose and the whole plan goes bad. We could have done empire retaliation
