Notice: Uninitialized string offset: 0 in Drupal\views\Plugin\views\filter\Date->acceptExposedInput() (line 139 of .../core/modules/views/src/Plugin/views/filter/Date.php).
It looks as though a variable in /core/modules/views/src/Plugin/views/filter/Date.php is being used without a check to ensure that the it exists.