default WooCommerce buttons disappeared

Hi there,
when we use the default WooCommerce button from product page the button itself dissapears. We need to deactivate the option an give the button an individual style so that it fits to the design of out website.
Times before the “default WooCommerce button” did work. The button appeared. From one day to the other (possibly with an update of the plugin or one other plugin) the button disappeared.
Furthermore the style of the font (Title and short description) changed: You can see the difference if you compare these two sites with two different styles of products displayed: https://tante-astrid.de/eltern-treff/ and https://tante-astrid.de/babys-erstes-jahr/. The last one (the affected product list is older).

Thanks and best regards, Jan

The page I need help with: [log in to see the link]