Poor Communication Kills
In case you think that might be my original idea, it is actually a trope at the addictive TV Tropes site.
https://tvtropes.org/pmwiki/pmwiki.php/Main/PoorCommunicationKills
That trope is about fictional characters who don't communicate vitally needed information to other characters, often with fatal results.
While watching Evil tonight, Thursday 11-14-19, I was reminded of some movie or program where the characters didn't share important information with other characters, often for no apparent reason, and bad things happened as a result.
I forget which movie or TV program the Evil episode reminded me of, but don't worry, there are plenty of other examples listed in the TV tropes page.
And in this Evil episode, "Vatican III", there was a bit of failure to communicate. The three representatives from the Vatican were distrustful of the three protagonists and tried to keep as much information as possible from them. And the three protagonists made some important discoveries about the business of the Vatican representatives, but there were no scenes where they shared that possibly vital information with the Vatican representatives who they were sort of working for. Even though that information concerned a possible end of the world!
And I didn't see an scenes where Dr. Bouchard showed her daughters the seals inscribed in the diaries given by Leland, and showed them her photos of the seals in the hierarchy, and showed them book pages where they are described as the seals of devils. She didn't tell them that Leland is either a devil who does evil things because he is a devil or else a crazy man who thinks he is a devil and and does evil things like devils do. She didn't tell them that Leland once told her that her four little girls were vulnerable to danger - in fact she acts like she forgot all about it.