There is a limit of 50 buttons on each card. Unfortunately a bug in HN v3.83 causes it to crash when this limit is exceeded.
There is an alternative to using many buttons though - use canavas:-
I have cards which appear to have many more than 50 buttons on them.
I simply use a canvas and load it with a graphic of the buttons all on one image.
Then use the mouse down event in the canvas to detect mouse X,Y coordinates and hence which "Button" has been clicked
For instance a full QWERTY keyboard can be implemented in ONE canvas.
You can also add some drawing commands to make it look as if a particular button has been pressed.
There is some use of canvases in the HN projects on our website.