Titans display a greyed out lock symbol and become unusable despite having 3 sins available, no active titans and having the skill tree requirements met.
I was playing Skirmish on the 3 player map: Acrophobia
None were being summoned, it was (or was meant to be) my 2nd titan, my 1st being a behemoth, my ally managed to summon several different titans (some twice or more).
My behemoth got killed. My behemoth and my ally's colossus were alive at the same time then my behemoth died and I was unable to summon another for the whole game whilst my ally could.
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