Z moves based off of attacks do not seem to be taking stat boosts into account, when they should. For example a Naganadel using Nasty Plot to get +2 SpAtk and then using Dragonium Z Draco Meteor on a Chansey should be doing about 50%.

+2 252 SpA Beast Boost Naganadel Devastating Drake (195 BP) vs. 0 HP / 252 SpD Eviolite Chansey: 319-376 (49.7 - 58.6%) -- 99.6% chance to 2HKO

Ingame however, the attack seemed to remove only 30% of Chanseys health, making me assume that Z moves don't seem to get the stat boosts.

252 SpA Beast Boost Naganadel Devastating Drake (195 BP) vs. 0 HP / 252 SpD Eviolite Chansey: 160-189 (24.9 - 29.4%) -- 100% chance to 4HKO

Hi. Thanks for the report. Unfortunately I'm not able to reproduce this. I tried using the following calculations before and after a Nasty Plot boost.

252 SpA Naganadel Devastating Drake (195 BP) vs. 252 HP / 4 SpD Eviolite Chansey: 201-237 (28.5 - 33.6%) -- 0.2% chance to 3HKO

+2 252 SpA Naganadel Devastating Drake (195 BP) vs. 252 HP / 4 SpD Eviolite Chansey: 399-471 (56.6 - 66.9%) -- guaranteed 2HKO

The damage in game seemed to reflect those calculations for the sets I used. Just the fact that after a boost the move did more damage shows that it is accounting for the boost, but the percentage damages also lined up so I don't see any issue. Even using the set you used with no HP and full SpD I got the right damage in-game.

If you encounter the problem again and can narrow down the problem to another issue, please make a new ticket and we can look into it again.