Hi Christian,
Can you please tell me if this is you catalogue page? All products should be at the same height.
My first guess is that your issue might probably caused by some conflicting plugin version. Can you please make sure that you have the latest theme version and that all recommended plugins are up-to-date? Finally, you could also consider clearing all activated caching system as well as your browser cache before investigating any further. If you want to read more on what browser cache is and how to clear it, here is an article that might help you: How to Clear Internet Cache in Every Major Browser.
In case this issue is still not solved by following the steps above, it’s best if we take a quick look at your website. Could you create a new website user for us please? If possible with administrator capabilities so we can make a quick check of your settings.
You can post the user name and password in your next reply and mark it as private to keep this between us.
Also, are we free to deactivate plugins for our tests? In this case, I invite you to make a backup before we investigate your website further in order to make sure you don’t loose any data if something goes wrong.
Thank you.