You can add this code to your site to de-register the Maps JS from the Events Calendar on the specified page ('lieux', but you can add more to that array if needed).
On my slimmed down copy of your site installed locally it works as expected.
And on a test site with the Events Calendar I cannot reproduce the problem that a map showing venues breaks if one or more of the venues is missing location data.
I'm at a bit of a loss as to what to do next, and am passing this back to my colleagues for further advice. I'll keep you posted.
I must apologise, my colleague asked me to create a new thread and assign it to him so that he can start from the beginning, and I missed that message.
Before I do, I have taken an updated copy of your site so that I can do some more debugging.
I've found a post where I can get the map to work, and another where it will not, and with that I might be able to identify an issue that I can replicate and which will make it much easier to identify the solution.
You should have received notice that I split this thread, where I have given an updated description of the problem, and I have re-assigned it to Beda from second-tier, as I have run out of things I can test.
So there is nothing more I can do here except once more apologise for the delay.