Also , except drag & drop method, you can use that command in chat [Pokemon1] , [Pokemon6] , numbers go from 1-6, depends on what slot you got the pokemon you want to link in chat.
I have noticed that too, but not on PC. This happens on the android client all the time , i got a lg g4 , it got 2560x1440 resolution so i have to check game zoom and increase GUI every time.