Submitting comments returns blank page

When someone submits a comment on one of my posts, it returns a blank page with this link:
https://www.twohorizons.nl/wp-comments-post.php

The comment doesn’t get displayed and I don’t receive an email notification. Does anyone know how to solve this? I’ve spend many hours searching for a solution within wordpress as well as on the internet but can’t seem to find one.

Thanks very much for your help!
Best,
Lennart

you can have a look at my site and test at https://www.twohorizons.nl