Larian's homebrew.
Original post, incorrect as I confused AB with Hex. Disregard.
Everywhere I looked (including your link), the damage type for Agonising Blast is never stated explicitly. The majority of the community seems to (again, implicitly) agree that it's also Force, just like the EB itself. This is somewhat supported by the wording at your link - "add your Charisma modifier to the damage it deals", which I suspect must be either an exact quote from PHB, or sufficiently close to it.
Larian, in their eternal quest to add as much "fun" to their games as possible without making them unsellable, changed the damage type for Agonising Blast to Necrotic, instead. I won't be surprised if Cracked Wall is immune to Necrotic damage, which should explain why you don't see the extra when you attack the wall, and should also explain why you do see the extra line when you attack a target which isn't immune to Necrotic. Whether it triggers an additional Concentration save, I honestly don't remember, but considering how much Larian hates Clerics, it probably does.
Why they did so? My guess is that they are changing rules for the sake of changing them. This has been explicitly stated by Swen way back in a day, when he said something along the lines of "we will take what we like from the rules, and change everything else because we aren't going to bow to rules imposed by others". Such a defiant rebel.
For the record, this change of damage type also means that Warlock's CHA doesn't matter when you attack walls or other stone pile-ups - the Agonising Blast's part is simply ignored.
Last edited by RutgerF; 04/03/22 05:31 AM.