Often times the Flash player has cached an out-dated version of the game. Clearing this from time to time can help with laggy play and things disappearing from your game.. In clearing this, it will force your browser to load the most current game from the Zynga servers.
Clear your Flash Cache by going here and choosing to "delete all sites" or scroll and find "assets.frontierville.zynga.com" and "delete website"
