Hey Bart,
Thanks for reaching out. I cannot currently recreate this problem.
I know you mention “all plugins and themes up to date,” but to help us investigate this, can you provide the following information?
1. Your site’s complete, un-edited “System Information” per the instructions of this article → https://theeventscalendar.com/knowledgebase/sharing-sys-info/
2. A link to your site’s main events page so that I can see the problem with those prev/next links live?
With this information we can proceed with investigating this and go from there.
Thank you!
George