Glad you like it! And sorry that you found a nasty bug. If the outline changes it means that its loading a different player slot (empty) for some reason and like you say, cannot move.
Can you tell me at what point it happens, if it is consistent or just completely random, often or rarely?, are you playing with a controller? Keyboard? If you are able to and do not mind try playing with keyboard or a different controller see if the issue continues.
Will take a look at the code and see what I can find. Again, sorry for the trouble and thank you for reporting the bug.