Thank you for all of this!
If you deactivate that Multilingual plugin temporarily, does anything improve with regards to this issue?
If not, then what about if you proceed with the rest of the steps in this guide → https://theeventscalendar.com/knowledgebase/testing-for-conflicts/?
I’m sorry to recommend these steps! 🙁 Unfortunately, I cannot produce this specific behavior and I notice many, many plugins on your site, so it’s possible there’s a code conflict here – a code conflict could be happening in numerous places on the site.
Let me know if you can do those steps, and if so what you find.
Thank you!
George