In Monster, if black premoved and white hasn't played his first of two moves yet, when white makes move then black's premove disappears.
If black premoved after white's first move on white's turn, then the premove works normally.
Monster black's premove disappears
Thanks for the investigate, this issue is linked to playstrategy.org/forum/playstrategy-feedback/pre-move-not-working-in-amazons#4
Currently the pre-move is being reset after an action in a game. Therefore it doesn't work correctly for multi-action games such as monster chess/amazons. We've raised a ticket to consider "fixing" this in the future.