Portal: cannot populate the game with bots on smaller servers

Late to the party but this is still a problem. Wanted to play a solo lobby in the new map to simply try it out, and practise the heli against trees as I did back in Zavod, but it refuses to work. Waiting at 13/20 'players', where it's myself and not enough bots backfilling. Not sure whether it's something i've missed on my end. Could do this easily in 2042