Filters not working any more

Hi, we have a whole set of websites with flexicontent using a date field which should be filtered. On most of them, the filters do not work any more since a recent update. The faceted filter shows all options with items - for example like this: 2019-11-24 (2), which indicates two items with that date, but when filtering, the no items message is displayed. I tried with the default template from flexicontent's latest version, but it's still the same.

Could you help?

Example URL that should output one item:
www.rkk-oberdorf.ch/termine?filter_17=2019-11-22

hello check format of date in field and compare with your url
i think the problem is here

I have activated the filter to test it, i.e. this URL was created by the filter form, not manually. Is it possible that the filter form creates a URL that isn't compatible with it?

For your information: I have many sites with exactly the same settings, only on one it works and on all the others not. All with the same settings though...
www.ref-liestal-seltisberg.ch/termine?filter_17=2019-11-20 here it works (you can click the calendar on the right)

Hello

this seems to be due to filter configuration

is your filter configured to a "specific value" (checkbox , radio) or is it configured as a range filter

You mean the filter settings of the field? I tried different ones with no effect. What would make sense is a dropdown or radio, i.e. single value. It's no range filter. Also, if I activate the filter and select one date, it behaves exacktly the same. Also, the filter settings are exactly the same on the page which works and on the ones that don't.
I think I ended up with a radio, as this is the configuration on the page that works.