Server flags in PRISM are 1740. Any button from any plugin won't display. I know that is very small info about problem, but it happens first time to me and everything else is ok.
Example code to send button
PRISM version 0.4.3
Example code to send button
$Msg = new Button(255, Button::$TO_ALL);
$Msg->Text('^3PRISM ^8Version ^7'.PHPInSimMod::VERSION.'^8.');
$Msg->T(IS_Y_MAX - IS_Y_MIN + 8)->L(IS_X_MIN)->W(IS_X_MAX)->H(8)->send();
PRISM version 0.4.3