I've been playing a Lurker Warlock for a few months now, and the subclass was recently canonized in Tasha's. I bought the subclass to simplify things on my end (I was making homebrew feats every time I got a new Patron feature and it was getting to be a headache), and I noticed that DnD Beyond now adds my charisma bonus to damage done by the tentacles. The text on the feature reads "On a hit, the target takes 1d8 cold damage, and its speed is reduced by 10 feet until the. start of your next turn." I have Agonizing Blast, which adds my charisma bonus to damage for my Eldritch Blast, which may be affecting the tentacles as well. I'm wondering if this is working as intended or if it's a bug in DnD Beyond. 

Given the wording - it shouldn't be getting any bonus. It says 1d8 cold - so that's all it should be. It's likely a bug that hasn't been ironed out yet. Tasha's has only just come out after all.

Yeah, that is a bug and needs to be reported in bug forum. It happens without agonizing blast too, so it is just a bug with the feature itself.

Good to know. Thanks everyone!