Hello @kumsangir

I have played the same game as yours here : playstrategy.org/TAczxut5 and I think I understand what happens.
Because the match is a correspondence game, each step of the multi-capture sequence has to be confirmed.
So you have to play f4-h4, confirm your move, then play h4-h2 and confirm again.
Let me know if this was the reason, or if you see any error in the console of your browser.