Good afternoon Merijn and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the all link not working properly on your website.
I would love to help you with this topic.
The main thing I am noticing is that your the Events Calendar and the Events Calendar Pro versions are currently not matching (4.4.5 vs 4.2.5).
It is very important that both versions “match” (in time) to ensure proper functioning.
Furthermore, since you are using WPML, the most optimized version we have for that purpose is 4.3.5 ( the Events Calendar ) and 4.3.4 (Pro).
I recommend reading the following: https://theeventscalendar.com/knowledgebase/downgrading-plugin-past-version/
If you do not wish to downgrade, you should upgrade Pro to 4.4.5
Of course, before any upgrade or downgrade, you should always to a database backup to be safe.
Let me know how that goes.
Best regards,
Geoff B.