I don't understand the problems you are having but another drawback to using the FEN to start a game is that it will produce a .pgn which will not work until you type in the missing moves. Using the FEN will also disable the [Explore] button in the vote chess games.
Best to report these problems to staff.
I've sent two vote chess games using a Fen from Endgame Lovers to Oracle and know I don't see them at all to accept or join the games! Oracle sees them. Also, a fen position game From Colle Group to Endgame Lovers has a game I can not join or accept from either group. ???
What am I missing? Regular Vote chess challenges I've had no problems with.