[whatbob1]

Yeah it was also mentioned in F/Z, but in the anime they cut off some lines with the Kotomine and Zouken conversation. where Zouken said there was something wrong with this Heaven's Feel and how a spirit like bluebeard could have been summoned.

Spoiler for zouken lines:

“I think the Tōsaka son and those of the Einsbern house are all idiots. If they remember the details from the last battle of the previous war, then they should understand that there is something odd with this fourth Heaven’s Feel, and be alert towards it."

"I saw through the battle for this round from the start. Truth be told, just by looking at that despicable Caster at the start of the War, we should have been able to tell that the summoning didn’t call forth a Heroic Spirit, but an evil spirit far removed from heroes. Without a doubt, something has begun to err within the Heaven’s Feel system. We need to solve this problem first.”