Ok, I’m going to list every change you need to make.
BP_PlayerController_ATBTT, BP_AbilitySystem, BP_Ability, BP_Ability_MoveAttack, BP_Unit (in two places for this one).
Unit switching logic is set up in the abilities you are using. In the example map, BP_Ability_MoveAttack is used, which has functionality for unit switching. You need to make one small change here to make sure you cannot switch to another unit if you do not have full AP (normally you are allowed to switch as long as you have at least 1 AP). The following nodes are in the Click comment box:
https://i.imgur.com/YfB4vqg.png
This seems to be working fine on my end, but I might not have tested thoroughly enough. If you run into problems can you give me the exact steps I need to do to replicate the problem? Tell me how many units there are, what their AI, faction and initiative settings are. What you click when etc. Send me a video if that is easier. But try to implement the stuff above first.
Edit: In other news, ladder jumping:
https://i.giphy.com/ZgUMSXx6MkL6Tesbfg.gif