Caching problem Firefox and Internet Explorer

Hi,

We have a problem on this website: https://www.classesdupatrimoine.brussels (FR)/ https://www.erfgoedklassen.brussels (NL)

I have added a new date (October 10th) for this event: "Expo : Le Patrimoine ? Un jeu d'enfant !/ Visite animée". When we normally refresh the page of the event: https://www.classesdupatrimoine.brussels/reserver/?id=41, the date should be added in the dropdown.

In Google Chrome everything showed well, like it should with the extra date. In Firefox the extra date is not visible after a normal refresh. Only after a HARD refresh we get to see the new date. This problem also happens in Internet Explorer sometimes.

So something is wrong here for some browsers and. This seems like a cache problem, but we don't know where it come from. We already cleared cache everywhere and asked our hosting. They say it's a problem somewhere in the website. So there is also no cache issue on server level.

Can you check please if there is a caching issue on the website?

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Thanks

Dieter