I tried this exact scenario and i was able to disconnect the player twice:
1. Both client and host are in game lobby
[host - admin screen, battle configuration]
2 + one cpu e.g. easy
(when game blocking rejoin to kicked player on 1vs1)
2. Host starts the game (with rejoin enabled)
3. Host presses ESC select disconnect menu and selects the player to drop and answers Yes
4. Client is dropped from game
5. Client reconnects in progress game (at this point you should already be able to drop the connected player)
5. yes, it is. in lobby before a rejoin it is possible at least one time (one time was tested)
Now you (client - "kicked player") have to make sure that you are on previously slot - in this case
second - blue.
(here almost always game put you to the third cpu slot,
[client - "kicked player" screen, not on previously slot.]
then you have to change your place to second slot manually)
[still client - "kicked player" screen, after manually changed slot]
6. Client clicks join in progress game
[client - "kicked player" screen]
[host - admin screen]
[host - admin screen, from now admin can't kick client anymore ]