For the weapon mods the little [!] icon appears in a soldier's list only if there's an empty slot for a mod.
The same isn't true for the PCS tab. After researching "Interchangeable PCSs" the orange [!] will remain permanently for every soldier that can equip PCSs. Once you finish that research, bHasNeurochipImplantsInInventory becomes the only condition for the [!] to show, which is practically always, unless you sell every extra PCS you can't immediately equip the moment you get it.
This isn't exactly a bug but it's not useful to have the game constantly tell the player that they can swap a soldier's equipped PCS with one that might even be worse, just because there is an unused PCS in the player's inventory.
For the weapon mods the little [!] icon appears in a soldier's list only if there's an empty slot for a mod. The same isn't true for the PCS tab. After researching "Interchangeable PCSs" the orange [!] will remain permanently for every soldier that can equip PCSs. Once you finish that research, bHasNeurochipImplantsInInventory becomes the only condition for the [!] to show, which is practically always, unless you sell every extra PCS you can't immediately equip the moment you get it. This isn't exactly a bug but it's not useful to have the game constantly tell the player that they can swap a soldier's equipped PCS with one that might even be worse, just because there is an unused PCS in the player's inventory.