When you have an event that opens a modal window, the button has strange behavior.
On my scene locally, I open popop modal windows after a click. But after several clicks the button it gradually becomes transparent to become invisible (the text is ok).
Then all the other buttons after some clicks gradually become invisible.
The button that are in containers (rectangle) do not have this problem.
On the PG, I use an alert () and the result is different, the button this resize progressively. I think both are binding problem and changes the button state after a blocking event (alert, prompt, popop modal ...)