Describe the bug
In both the default and manually specified sortable_fields: ['fields.date'], the collection (events) is sorted by their file name and not their front matter date. This is the repository https://github.com/techworkersco/twc-site-berlin, and the admin-configs

In either situation, the files "sorted" by date, show collection of events 1.md, 10.md, 11.md, 2.md, 21.md etc..

Expected behavior
I'd expect that the date column is used to sort the files