Hi, I have a similar problem. Works on Chrome but not in Firefox. I have isolated the problem and it seems to have something to do with TranslatePress plugin: When I am using other than default language browser is not able to load the product in the bundle selection. Disabling the plugin helps of course but it is not really an option as I need to have my site also another language than the default.
Also the loading takes up to 2 seconds even with the TranslatePress plugin disabled which is, to me at least, a very long time.