Hi PeterMeyer.
I noticed the filter bar trying to work but then the results below it don’t seem to be any different — so, in your words, “doesn’t work”. 🙂
Could you try changing your “Datepicker Date Format” to “2015-01-15” and testing if that makes Filter Bar work?

Get to it from the Events Settings -> Display -> “Date Format Settings” section
(I’d expect the Filter Bar to work just fine with any of those settings but I thought it might just be something quick and easy to try.)
If it doesn’t help, I’ll have to suggest deactivating all non-Modern Tribe plugins and testing with the Twenty Fifteen theme and seeing if the issue persists.
Please let me know how it goes. Thanks.